TiPS - June 2990 [Vol. 2 ZJ
231
Peter H. Andersen, Jay A. Gingrich, Michael D. Bates, Allen Dearry, Pierre Falardeau, Susan E. Senogles and Marc G. Caron The DIIDt dopamine receptor classification is widely accepted. However, intense investigative efforts over the last several years using pharmacological, biochemical and behavioral approaches have produced rLsults that are increasingly difficult to reconcile with the existence of only two dopamine receptor subtypes. Recent developments, including cloning of the cDNAs and/ or genes for several members of the large family of G-protein-coupled receptcrs, have revealed that heterogeneity in the pharmacctogical or biochemical characreristics of individual receptors ofterz indicates the presence of previously unsuspected moIecular subtypes. In this article, Marc Caron and colleagues have assembled the main lines of evidence that suggest the presence of several novel subtypes for both Dr and D2 dopamine receptors and predict that molecular cloning will, in the near future, confirm their existence. It is more than 30 years since dopamine was shown to be a neurotransmitter in the CNS. In the early 197Os, many studies showed the effects of dopamine to be inconsistent with the concept that a single receptor mediates all the physiological functions of this catecholamine. Thus at that time it was suggested that the existence of two dopamine receptor populations or subtypes (termed Dr and Dz) could account for most, if not all, of the findings in the literature. Although others have been proposed, the Di/Dz receptor classification is still the most widely recognized (for review, see Ref. 1). Dopamine D1 receptors act via stimulation of adenylyl cyclase, whereas Dz receptors are either
P. H. Andersen is Director of Biochemical Pharmacology at Novo Nordisk A/S, CNS Division, t&o ABe, DK-2880 Bagsvaerd. Denmark; 1. A. Gingrich and M. D. Bates are Graduate Students at the Department of Cell Biology, A. Deary is Assistant Medical Resee:;.‘, ? SKF77434 > SKF38393 >> 5.6-ADTN = 6,7-ADTN > dopamine
NO1 12 = NO756 > fluperlapine = clozapine = SCH23390 = cis-flupentixol r bulbocapnine >> sulpiride
t adenylyl cyclase
amygdala, strfatum, frontal cortex, nucleus accumbens
SKF75670 > SKF38393 = SKF77434 >> dopamine = 6,7-ADTN > 5.6-ADTN
SCH23390 = NO1 12 = NO756 = cis-flupentixol >> clozapine > fluperlapine > bulbocapnine >>> sulpiride
? t polyphosphoinosilide hydrolysis
mesenteric bed
fenoldopam > dopamine > SKF38393
t adenylyl cyclase
splenic artery, renal cortex
dopamine >> SKF38393 = fenoldopam
SCH23390 > butaclamol = bulbocapnine > sulpiride >> haloperidol SCH23390 > butaclarnol > bulbocapnine > haloperidol >5 sulpirfde
renal cortex
no conclusive data
SCH23390 = sulpiride
? t phospholipaseC
striatum. limbic areas, retina
no conclusive data
spiperone > haloperidol > sulpiride = clozapine spiperone > haloperidol >> sulpiride = clozapine
Peripheral D,
T adenylyl cyclase
I
1 adenylyl cyclase open K’ channels ? 1 phospholipase C ? 1 Ca” channels ? J polyphosphoinositide hydrolysis
strialum, pituitary, retina
no conclusive data
heart
DP-5,6-ADTN > DP-8.7-ADTN > dopamine >> SKF38393 = fenoldopam
haloperidol > cis-flupentixol > sulpiride >> SCH23390
1 adenylyl cyclase
mesenteric artery
DP-5,6-ADTN > dopamine = DP-6,7-ADTN > fenoldopam >> SKF38393
haloperidol = sulpiride >> cis-flupentixol = SCH23399
no data
D2
Perioheral
4
Transmembrane signalling
agonists
Anatomical location
of receptor number and of affinity for agonists and
Methods used for subtype identification and definition have changed markedly during the last 50 years. Initially, a receptor subtype was defined as a receptor with a different pharmacological profile. In the early years, ‘classical’ pharmacological methods created the basis for this receptor subtype definition. Later, electrophysiological recordings of cellular responses were used to identify receptor subtypes. The discovery of intracellular chemical messengers - second messengers such as CAMP - led to yet another basis for subtype definition. In the early 1970s. the technique of radioligand binding was introduced. Unlike functional measures of receptor activation, radioligand bAndingis simple and rapid and allows direct quantification both
Rf2captW family
Subtype
ADENOSlNE=----1
2
0, 4’
aelaheal D. rx------peripheral 0, others ?
WPAMINE
1
LHlhCG’ GLYCOPROTEIN HORMONE
=-i
MUSCARINICCHOLINERGIC ---I
OPSIN
FSH TSH ml‘ m2’ m3’ m4‘ m5 rhodopsin’ red opsin’ blue opsin’ green opsin’
antagonists. These methods have often been used in combination to create a cohesive picture of receptor subtypes, characterized by their localization, ligandbinding properties, biochemical responses and physiological effects. Application of molecular biological tools to receptor research in the 1980s has added a new dimension to our understanding of receptor classification and subtype definition. cDNAs and/or genes for numerous receptors have been isolated and sequenced, and this has provided much information on the structure and function of receptor families and their subtypes. Given the diversity of substances that interact with receptors, it is somewhat surprising that, on the basis of their DNA sequences, most receptors can easily be categorized into only a few superfamilies, such as growth factor receptors and G-protein-coupled receptors. To date, the latter is the most extensive superfamily, incorporating severa! smaller families of receptors such as the adrenoceptors, and muscarinic acetylcholine and 5-HT receptors and the visual opsins (see Fig.). Another surprising trend to emerge from the molecular biological approach is that within each of these smaller families, a large number of highly homologous members or subtypes appears to exist. In many instances, the existence of multiple subtypes was not postulated before their identification by cloning techniques. This proliferation of subtypes is most readily apparent in the muscarinic receptor family, where five members have been identified, when only two had previously been characterized phannacologitally. Multiple subtypes are also emerging for adrenoceptors and 5-HT receptors and will undoubtedly do so for other receptor families as well. Molecular biology has also created a new basis for the definition of receptor subtypes. Previously, the pharmacological profile of a receptor constituted the major criterion for this definition. [Indeed this is the basis for ciassification in the TiPS Receptor Nomenclature Supplement - ed.] Now molecular biology permits receptor subtype definition based on the isolation and characterization of distinct receptor genes or their cDNAs. Thus, receptor proteins that are encoded by different genes should perhaps become the basis of this definition and be accepted as sufficient evi.Lence for the existence of new subtypes even though only minor pharmacological differences might exist. A special case which has been documented for the Dz doparnine receptor is when two forms of the same receptor arise by alternative splicing of an exon in the same gene13. In such a case, the two forms of the receptor should be referred to as isoreceptors of that particular subtype.
1 some members of the G-protein-ooupled receptor superfamily. ‘Subtype for which a cDNA and/or gene has been cloned; +two isoreceptors cloned. Fi.
which are pharmacologically very similar to the central D1 and D2 receptors described above. Some differences have, however, now been identified (see below). More-
D. K. et al. (1989) Pm. Nat2 Acad. Sci. USA 86, 9762-9766 2 Monsma, F. J., McVittie, L. D., Gerfen, C. R., Mahan, L. C. and Sibley, D. R. (1989) Nature 342,926-929 3 Giros, 8. et al. (1989) Nature 342,923-926 Grady,
over, atypical profiles of some Dr and D2 receptor agonists and antagonists have suggested that there may be more than one population of each subtype in the peri-
Thus two populations of peripheral D1 receptors have been identified on the basis of sensitivity to sulpiride4r. Both receptor popmatrons are poteiitly blocked 1 .’
phe@l.
TiPS
-fzfne 2990 [Vol.
235
111
by SCH23390, but only the receptors sensitive to sulpiride are potently stimulated by SKF38393 and fenoldopamql. Two different second messenger responses have been reported for the peripheral D1 receptor: stimulation of adenylyl cyclase and stimulation of phospholipase C (Refs 42-44). Furthermore, differences in pharmacology may exist within the cyclase-coupled Dt receptor population. For example, dopaminestimulated adenylyl cydase in renal cortex is potently inhibited by sulpiride*z, whereas dopaminestimulated adenylyl cyclase in the mesenteric artery is noP3. Further, ph~acological chara~eristics of D1 receptor binding to membranes from renal cortex do not Match those of dopamine-stimulated adenylyl cyclase42,45,46.Both peripheral D1 populations coupled to adenylyl cyclase differ from the D1 receptor in the CNS in that the peripheral receptors have a high affinity for bulbocapnine (mesenteric artery) and sulpiride (renal while these comcortex)**,“, pounds exhibit very low affinity for central D1 receptors*. Also, the D1 receptor sites labe!ed by radio&and binding in renal tissue@eM disp!ay s 20-fold lower affinity for SCH23390 than the corresponding sites in the CM. Similarly, two peripheral D2 receptor populations have been identified4*. CIne population has high affinity for cis-flupentixol and both the 5,6- and 6,7-NADTN derivatives; by contrast cisflupentixol is inactive and only the 5,6-ADTN derivative shows high affinity for the other type41. The D:! receptor located in the mesenteric artery is negatively coupled to adenylyl cyclase43 and shows characteristics identical to the subtype described in heart?. No other second messenger responses to peripheral Dz receptor stimulation have been reported. It is not yet known whether peripheral D2 receptors differ from their CNS counterparts. However, the peripheral D2 receptor showing low affinity for cis-flupentixol has no obvious counterpart in the CNS. These findings are consistent with the existence of multiple receptor subtypes dopamine within the cardiovascular and renal systems. For peripheral DI ,.__L_l ---LJ”-_r^ receptiX%, %VQpua~~~iia JuucyysJ
that stimulate adenylyl cyclase can be identified on the basis of their differing sensitivities to sulpiride. In addition, D1-mediated stimulation of phospholipase C has been reported. However, this second messenger response has not been well characterized pharmacologically. Thus, at least two and possibly three peripheral D1 subtypes may exist (Table I). For the peripheral DZ receptor, two subtypes can be identified by differing potencies of flupentixol and aminotetralines. No differences in second messenger coupling have yet been documented for the cardiovascular or renal LIZ rezeptars. Furthermore, at least one subtype (the flupentixol-sensitive type) may have an identical counterpart in the CNS. cl
q
!I
We have hi~lighted some of the recent findings that appear to be inconsistent with the simple two dopamine receptor hypothesis put forth over a decade ago. Given the recent discoveries of numerous new subtypes in other receptor families using a molecular biological approach, it is tempting to speculate that the inconsistencies in pharmacological and functional responses that we have described here presage the existence of additional dopamine receptor subtypes. Dopamine plays a major role in numerous physiological functions in the periphery as well as in the CNS. In particular, dopamineresponsive cells are clearly implic&ted in the etiology and/or treatment of disorders such as schizophrenia and parkinsonism. Each of these diseases may be treated with agents that interact with dopamine receptors. However, these drugs have serious side-effects, some of which may be due to their interactions with dopamine receptor subtypes other than those that produce the desired therapeutic effect. For example, the antipsychotic drugs currently in use cause various motor dysfunctions and h~e~rolactinemia, while the drugs used to treat parkinsonism can cause nausea and vomiting, choreiform movements, psychiatric disturbances and cardiovascular problems. A clearer understanding of which -.-LL,.....~ I,.FYIIl&L .,.,.-ii:-&, .yLu..~uLu-’ ..~.+&.rt~tnh..&-._ JUr;&Yt.JSJ F”, I--
logical effects would promote development of more specific drugs and hence improve treatment of these disorders. The cloning and characterization of the relevant dopamine receptor subtype(s) will provide the tools necessary to achieve these aims. References
Clark,D. and White, F. J. (1987) Synapse
1, 347-388 Lefkowitz, R. J., Kobilka, B. K. and Camn, M. G. (1989) Biockem. Phannacol. 38.2941-2948 Hyttel. J. (1984) in 7th Symposium on Medicinal Chemistry (DahEbaum, R. and Nidsson, J. L. G., eds), pp. 42-39, Swedish Pha~a~utic~ Press Andersen, P. H. and Braestrup, C. (1986) J. Neumchent. 47,1822-1831 Andersen, P. H. et al. (1988) Sot. Neurusci. Abstr. 378.13 Mailman, R. 8. ef al. (1986) in Netrrobiology of Cenfraf D,-Receptors (Breese, G. R. and Creese, I., eds), pp. 5X72, Plenum Press 7 Dawson, T. M., Gehfert, D. R., McCabe, R. I’., Barnett, A. and Wamsley, J. K. (1986) J. Neurosci. 6, 2352-2365 8 Walaas, S. I. and Greengard, P. (1984) J. Neurosci. 4,84-98 9 Johansen, P. A. and White, F. J. (1988) Sot. Neurosci. Abstr. 377.7 10 Waddington, J. L., O’Boyle, K. M. and Murray, A. M. (1988) Ne~~mche~. I&. 13, F326 11 Amt, J., Hytfel, J. and Meier, E. (1988) Eur. J. Pharmacol. 155,37-46 12 Cameron, D. L. and Cmcker, A. D. (1988) Neurosci. Left. 90, 165171 13 Monsma, F. J., Burch, R. H., Sibley, D. R. and Mahan, L. C. (1989) Sot. Neurosci. Abstr. 171.9 14 DeCamiUi, I’., Macroni, 0. and Spada, D. (1979) Nature 278,252-254 15 Kelley, E. and Nahomki, S. R. (1987) Naunyn-Schmiedeberg’s Arch. Pharmacol. 335, 508-512 16 Freedman, J. E. and Weight, F. F. (1988) Proc. Nat1 Acad. 5n‘. USA 85, 3618-3622 17 Israel, M. M., Jaquet, P. and Vincent, J. D. (1985) E~~acr~nof~~ 117,1446-1455 18 Canonico, P. L., Valdenego, C. A. and Macleod, R. M. (1983) Endocrinology 113. 7-14 19 Vallar, L., Vicentini, L. M. and Meldolesi, J. (1988) J. Biol. Ckem. 263, lOl27-10134 20 Bockaert, J., Joumot. L. and Enjalbert, A. (1988) J. Recegt. Res. 8‘225-243 21 Wolf, M. E. and Roth, R. H. (1987) in Dupamine Receptors (Geese, I. and Fraser, C. M., eds). pp. 4%96, A. R. Liss 22 Clark, D., Hjorth, S. and Carlsson, A. (1985) J. Neural Tmasm. 62, l-5.: 23 Skirboll, L. R., Grace, A. A. and Bunney, B. S. (1979) Science 296,8@-82 24 Starke, K., Spath, L., Lang, J. D. and Adelung, C. (1983) Naunyn-Schmjedeberg’s Arch. Pha~aco~. 323,298-306 25 Clark, D., Hjorih, S. and C&sson, A. (1985) J. Neural Transm. 62,171-207 26 Meller, E., Bohmaker, K., Namba, Y., Friedhoff, A. J. and Goldstein, M. (1987) Mol. Pharmacol. 31,592-598 27 Herdon, H. (1988) Eur. 1. Pkarmacol. 15% x5-:16
TiPS - fune 1990 fVol. 121
236 28 Kohler, C., Haglund, L., Ogren, S-O. and Angeby, T. (1981) 1. Newal Trunsm. 52, 163-173 29 Bischoff, S., Bittiger, H., Delini-Stula. A. and Orbnan, R. (1981) Eur. j. Pftarmacol. 79,225232 30 White, F. J, and Wong, R. Y. (1983) Science 221,105&1057 31 Kohler, C. and Fahlberg, K. (1985) J. Neural Trunsm. 63,39-52 32 McConigle. P., Wax, M. B. md Molinoff, P. B. (1988) Inoesf. Ophthalmot. Vis. Sci. 29.687694 33
Bunzow. J. R. et
a?.
(1988) N&we 336,
7R?-rn?
.-_ .-.
34 Albert, P. R., Neve. K. A., Buruow, J. R. and Civelli, 0. (19%) [. Biot. Chem. 265, 2098-2104 35 Weine, D. M. and Brann,
M. R. (1989) FESS Ltt. 253,207-213 36 Grandy, D. K. et al. (1989) Proc. Nntl
Acad. Sci. USA a&9762-9766 37 Monsma, F. J., McVittie, L. D., Gerfen, C. R., Mahan, L. C. and Sibley, D. R. (1989) Nature 342, 926-929 38 Giros, 8. et ai. (1989) Natire 342,923-926 39 Dal Toso, R. et at. (1989) EM90 1. 8, 4025-4035 40 Todd, R. D., Khurana, T. S., Sajovic. I’., Stone, K. R. and O’Malley, K. L. (1989) Proc. Nat1 Acad. Sci. USA 86, 10134-10138 41 Hilditch, A. and Drew, G. M. (1985) Trends Dhnrmacoi. Sci. 6.396-400 42 BaIdi, E., Pupilli, C., Amenta, F. and ManneUi, M. (1988) Eur. 1. P}~armffcoi. 149,351-?&l 43 Missale. C., Castelletti,
L., Memo, M., Carruba, M. 0. and Spano. P. F. (1985) 1. Cardiovasc. Pharmacof. 11, 643-650 44 Felder, C. C., Jose, P. A. and Axelrod, J. (1989) 1. Pharmacol. Exp. Ther. 248,
171-175 45 Hughes,
A. and Sever, P. (1988) Bio38,781-785 46 Zdilar, D. and Lackovic, S. (1989) Eur. I. Phnm! zs!. ?64,:59-162 &em.
Pharmacol.
ADTN: dipropylaminotetraline NOll2: R(f)-8-chloro-7-hydroxy-3methyl-5-(7-benzofuran)-2,3,4,5-tetra hydra-lHJ-benzapine N0756: R(f)-8-chloro-7-hydroxy-3methyl-5-[7-(2,3-dihydro)benzofuran] 2~,4,S-te~ahydro-lH-3-benzapine .%X233% 7-~loro-2,3,4,5-te~ahydro-3me~yl-5-phenyl-lH-3-benza~epine-7-ol SKF38393: 2,3,4,5-tetrahydro-7,8dihydroxy-l-phenyl-lH-3-benzazepine SKF75670: 2,3,4,5-tetrahydro-3-methyl-7,8dihydroxy-l-phenyl-lH-3-benzazepine SKF77434: 2,3,4,5-tetrahpdro-3-al!yl-7.8dihydroxy-l-phenyl-lH-3-benzazepine
work; however, roots are evident in Magnus’s laboratory: there, in 1923 a remarkable little textbook* (Fig. 1) on pharmacology, ahead of its time, was written by W. Storm van Leeuwen (1882-1933). His career was unconventional for a scientist: after early retirement as a cavalry officer he studied medicine, he came to work with Magnus and in 1920 became professor of pharmacology in Leiden. His interest P~zu~a~~o~ is an active sport in the ~et~erlan~. Each of the country’s shifted to the immunological aseight universities has a depa~en~ o~pha~u~~lo~ and there are at least pects of allergy. When the universix government-operafed research institutes. This activity owes a debt to sity board rejected his request for the long history of the discipline. Rather than cataloguing today’sresearch hospital beds at the university or providing a rigid historical study, Erik Noach presents a pharmacolhospital, he founded his own ogist’s perspectiveon the sources and directions of pharmacological private clinic for allergic diseases, research in the ~e~her~an~. which attracted many - mostly foreign - patients. The good citizens of Leiden respectfully ALTHOUGH PHARMACOLOGY did not develop as a distinct watched the awkward high strucdiscipline until the early years of this century, there were several tures near the clinic where ‘undrug investigators working in the Netherlands before that time. polluted’ (by pollen) air was taken Among them were the internist B. J. Stokvis (1834-1902), professor in and filtered for the ‘allergenin Amsterdam, who wrote a textbook of materia medical (Fig. 1) free’ patient rooms. After his eariy which is still fascinating: to read, and C. A. Pekelha~g (l&%8- death in 1933 allergology was con1922) in Utrecht, who wai origtinued by clinical investigators. Heidelberg, was mainly interested inally a physiological chemist Magnus’s successor was his in direct effects of drug molecules but also worked on anatomy, pupil U. G. Bijlsma (1892-1977). In on organ functions. Hence, experhistology, general pathology addition to his own cardiovasiments with isolated preparations and pharmacology. were methodologically of prime cular investigations, he mainHowever, experimental pharmatained relations with the pharmaimportance; the ‘Magnus apparcology flowered with the appointatus‘ for in-vitro studies of smooth ceutical firm of Brocades (today, ments as professors of pharmamuscle preparations is still in use. after mergers, Gist-Brocades). cology of Rudolph Magnus (1873This ultimately led to the estabHis successors evolved this ap1927) in 1908 in Utrecht, and Ernst lishment of a pharmacochemistry proach to research on drugLaqueur (1880-1947) in 1920 in department there, led by W. Th. receptor interactions, structureAmsterdam. Their heritage can be Nauta, who later founded a simiactivity relationships and drug traced in Dutch pha~acolo~ up design. lar laboratory at the (P~testant) Magnus’s ‘scientific to the present day. Both came Free University in Amsterdam. He grandson’ E. J. AriiZns and the from Germany, but they had few latter’s co-workers - especially J. was succeeded by the present incommon scientific interests. M. van Rossum and A. M. Simonis cumbent H. Timmerman. The - made fundamental contributions ‘receptorologist’ J. Zaagsma in The influence of Magnus to this area. It is commonly asGroningen is another of Nauta’s Magnus (Fig. 2), who had worked sumed that ArKns’s studies are disciples although he was also in R. Gottlieb‘s laboratory in mainly inspired by A. J. Clark’s strongly influenced by Ariens.
231
Peter H. Andersen, Jay A. Gingrich, Michael D. Bates, Allen Dearry, Pierre Falardeau, Susan E. Senogles and Marc G. Caron The DIIDt dopamine receptor classification is widely accepted. However, intense investigative efforts over the last several years using pharmacological, biochemical and behavioral approaches have produced rLsults that are increasingly difficult to reconcile with the existence of only two dopamine receptor subtypes. Recent developments, including cloning of the cDNAs and/ or genes for several members of the large family of G-protein-coupled receptcrs, have revealed that heterogeneity in the pharmacctogical or biochemical characreristics of individual receptors ofterz indicates the presence of previously unsuspected moIecular subtypes. In this article, Marc Caron and colleagues have assembled the main lines of evidence that suggest the presence of several novel subtypes for both Dr and D2 dopamine receptors and predict that molecular cloning will, in the near future, confirm their existence. It is more than 30 years since dopamine was shown to be a neurotransmitter in the CNS. In the early 197Os, many studies showed the effects of dopamine to be inconsistent with the concept that a single receptor mediates all the physiological functions of this catecholamine. Thus at that time it was suggested that the existence of two dopamine receptor populations or subtypes (termed Dr and Dz) could account for most, if not all, of the findings in the literature. Although others have been proposed, the Di/Dz receptor classification is still the most widely recognized (for review, see Ref. 1). Dopamine D1 receptors act via stimulation of adenylyl cyclase, whereas Dz receptors are either
P. H. Andersen is Director of Biochemical Pharmacology at Novo Nordisk A/S, CNS Division, t&o ABe, DK-2880 Bagsvaerd. Denmark; 1. A. Gingrich and M. D. Bates are Graduate Students at the Department of Cell Biology, A. Deary is Assistant Medical Resee:;.‘, ? SKF77434 > SKF38393 >> 5.6-ADTN = 6,7-ADTN > dopamine
NO1 12 = NO756 > fluperlapine = clozapine = SCH23390 = cis-flupentixol r bulbocapnine >> sulpiride
t adenylyl cyclase
amygdala, strfatum, frontal cortex, nucleus accumbens
SKF75670 > SKF38393 = SKF77434 >> dopamine = 6,7-ADTN > 5.6-ADTN
SCH23390 = NO1 12 = NO756 = cis-flupentixol >> clozapine > fluperlapine > bulbocapnine >>> sulpiride
? t polyphosphoinosilide hydrolysis
mesenteric bed
fenoldopam > dopamine > SKF38393
t adenylyl cyclase
splenic artery, renal cortex
dopamine >> SKF38393 = fenoldopam
SCH23390 > butaclamol = bulbocapnine > sulpiride >> haloperidol SCH23390 > butaclarnol > bulbocapnine > haloperidol >5 sulpirfde
renal cortex
no conclusive data
SCH23390 = sulpiride
? t phospholipaseC
striatum. limbic areas, retina
no conclusive data
spiperone > haloperidol > sulpiride = clozapine spiperone > haloperidol >> sulpiride = clozapine
Peripheral D,
T adenylyl cyclase
I
1 adenylyl cyclase open K’ channels ? 1 phospholipase C ? 1 Ca” channels ? J polyphosphoinositide hydrolysis
strialum, pituitary, retina
no conclusive data
heart
DP-5,6-ADTN > DP-8.7-ADTN > dopamine >> SKF38393 = fenoldopam
haloperidol > cis-flupentixol > sulpiride >> SCH23390
1 adenylyl cyclase
mesenteric artery
DP-5,6-ADTN > dopamine = DP-6,7-ADTN > fenoldopam >> SKF38393
haloperidol = sulpiride >> cis-flupentixol = SCH23399
no data
D2
Perioheral
4
Transmembrane signalling
agonists
Anatomical location
of receptor number and of affinity for agonists and
Methods used for subtype identification and definition have changed markedly during the last 50 years. Initially, a receptor subtype was defined as a receptor with a different pharmacological profile. In the early years, ‘classical’ pharmacological methods created the basis for this receptor subtype definition. Later, electrophysiological recordings of cellular responses were used to identify receptor subtypes. The discovery of intracellular chemical messengers - second messengers such as CAMP - led to yet another basis for subtype definition. In the early 1970s. the technique of radioligand binding was introduced. Unlike functional measures of receptor activation, radioligand bAndingis simple and rapid and allows direct quantification both
Rf2captW family
Subtype
ADENOSlNE=----1
2
0, 4’
aelaheal D. rx------peripheral 0, others ?
WPAMINE
1
LHlhCG’ GLYCOPROTEIN HORMONE
=-i
MUSCARINICCHOLINERGIC ---I
OPSIN
FSH TSH ml‘ m2’ m3’ m4‘ m5 rhodopsin’ red opsin’ blue opsin’ green opsin’
antagonists. These methods have often been used in combination to create a cohesive picture of receptor subtypes, characterized by their localization, ligandbinding properties, biochemical responses and physiological effects. Application of molecular biological tools to receptor research in the 1980s has added a new dimension to our understanding of receptor classification and subtype definition. cDNAs and/or genes for numerous receptors have been isolated and sequenced, and this has provided much information on the structure and function of receptor families and their subtypes. Given the diversity of substances that interact with receptors, it is somewhat surprising that, on the basis of their DNA sequences, most receptors can easily be categorized into only a few superfamilies, such as growth factor receptors and G-protein-coupled receptors. To date, the latter is the most extensive superfamily, incorporating severa! smaller families of receptors such as the adrenoceptors, and muscarinic acetylcholine and 5-HT receptors and the visual opsins (see Fig.). Another surprising trend to emerge from the molecular biological approach is that within each of these smaller families, a large number of highly homologous members or subtypes appears to exist. In many instances, the existence of multiple subtypes was not postulated before their identification by cloning techniques. This proliferation of subtypes is most readily apparent in the muscarinic receptor family, where five members have been identified, when only two had previously been characterized phannacologitally. Multiple subtypes are also emerging for adrenoceptors and 5-HT receptors and will undoubtedly do so for other receptor families as well. Molecular biology has also created a new basis for the definition of receptor subtypes. Previously, the pharmacological profile of a receptor constituted the major criterion for this definition. [Indeed this is the basis for ciassification in the TiPS Receptor Nomenclature Supplement - ed.] Now molecular biology permits receptor subtype definition based on the isolation and characterization of distinct receptor genes or their cDNAs. Thus, receptor proteins that are encoded by different genes should perhaps become the basis of this definition and be accepted as sufficient evi.Lence for the existence of new subtypes even though only minor pharmacological differences might exist. A special case which has been documented for the Dz doparnine receptor is when two forms of the same receptor arise by alternative splicing of an exon in the same gene13. In such a case, the two forms of the receptor should be referred to as isoreceptors of that particular subtype.
1 some members of the G-protein-ooupled receptor superfamily. ‘Subtype for which a cDNA and/or gene has been cloned; +two isoreceptors cloned. Fi.
which are pharmacologically very similar to the central D1 and D2 receptors described above. Some differences have, however, now been identified (see below). More-
D. K. et al. (1989) Pm. Nat2 Acad. Sci. USA 86, 9762-9766 2 Monsma, F. J., McVittie, L. D., Gerfen, C. R., Mahan, L. C. and Sibley, D. R. (1989) Nature 342,926-929 3 Giros, 8. et al. (1989) Nature 342,923-926 Grady,
over, atypical profiles of some Dr and D2 receptor agonists and antagonists have suggested that there may be more than one population of each subtype in the peri-
Thus two populations of peripheral D1 receptors have been identified on the basis of sensitivity to sulpiride4r. Both receptor popmatrons are poteiitly blocked 1 .’
phe@l.
TiPS
-fzfne 2990 [Vol.
235
111
by SCH23390, but only the receptors sensitive to sulpiride are potently stimulated by SKF38393 and fenoldopamql. Two different second messenger responses have been reported for the peripheral D1 receptor: stimulation of adenylyl cyclase and stimulation of phospholipase C (Refs 42-44). Furthermore, differences in pharmacology may exist within the cyclase-coupled Dt receptor population. For example, dopaminestimulated adenylyl cydase in renal cortex is potently inhibited by sulpiride*z, whereas dopaminestimulated adenylyl cyclase in the mesenteric artery is noP3. Further, ph~acological chara~eristics of D1 receptor binding to membranes from renal cortex do not Match those of dopamine-stimulated adenylyl cyclase42,45,46.Both peripheral D1 populations coupled to adenylyl cyclase differ from the D1 receptor in the CNS in that the peripheral receptors have a high affinity for bulbocapnine (mesenteric artery) and sulpiride (renal while these comcortex)**,“, pounds exhibit very low affinity for central D1 receptors*. Also, the D1 receptor sites labe!ed by radio&and binding in renal tissue@eM disp!ay s 20-fold lower affinity for SCH23390 than the corresponding sites in the CM. Similarly, two peripheral D2 receptor populations have been identified4*. CIne population has high affinity for cis-flupentixol and both the 5,6- and 6,7-NADTN derivatives; by contrast cisflupentixol is inactive and only the 5,6-ADTN derivative shows high affinity for the other type41. The D:! receptor located in the mesenteric artery is negatively coupled to adenylyl cyclase43 and shows characteristics identical to the subtype described in heart?. No other second messenger responses to peripheral Dz receptor stimulation have been reported. It is not yet known whether peripheral D2 receptors differ from their CNS counterparts. However, the peripheral D2 receptor showing low affinity for cis-flupentixol has no obvious counterpart in the CNS. These findings are consistent with the existence of multiple receptor subtypes dopamine within the cardiovascular and renal systems. For peripheral DI ,.__L_l ---LJ”-_r^ receptiX%, %VQpua~~~iia JuucyysJ
that stimulate adenylyl cyclase can be identified on the basis of their differing sensitivities to sulpiride. In addition, D1-mediated stimulation of phospholipase C has been reported. However, this second messenger response has not been well characterized pharmacologically. Thus, at least two and possibly three peripheral D1 subtypes may exist (Table I). For the peripheral DZ receptor, two subtypes can be identified by differing potencies of flupentixol and aminotetralines. No differences in second messenger coupling have yet been documented for the cardiovascular or renal LIZ rezeptars. Furthermore, at least one subtype (the flupentixol-sensitive type) may have an identical counterpart in the CNS. cl
q
!I
We have hi~lighted some of the recent findings that appear to be inconsistent with the simple two dopamine receptor hypothesis put forth over a decade ago. Given the recent discoveries of numerous new subtypes in other receptor families using a molecular biological approach, it is tempting to speculate that the inconsistencies in pharmacological and functional responses that we have described here presage the existence of additional dopamine receptor subtypes. Dopamine plays a major role in numerous physiological functions in the periphery as well as in the CNS. In particular, dopamineresponsive cells are clearly implic&ted in the etiology and/or treatment of disorders such as schizophrenia and parkinsonism. Each of these diseases may be treated with agents that interact with dopamine receptors. However, these drugs have serious side-effects, some of which may be due to their interactions with dopamine receptor subtypes other than those that produce the desired therapeutic effect. For example, the antipsychotic drugs currently in use cause various motor dysfunctions and h~e~rolactinemia, while the drugs used to treat parkinsonism can cause nausea and vomiting, choreiform movements, psychiatric disturbances and cardiovascular problems. A clearer understanding of which -.-LL,.....~ I,.FYIIl&L .,.,.-ii:-&, .yLu..~uLu-’ ..~.+&.rt~tnh..&-._ JUr;&Yt.JSJ F”, I--
logical effects would promote development of more specific drugs and hence improve treatment of these disorders. The cloning and characterization of the relevant dopamine receptor subtype(s) will provide the tools necessary to achieve these aims. References
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1, 347-388 Lefkowitz, R. J., Kobilka, B. K. and Camn, M. G. (1989) Biockem. Phannacol. 38.2941-2948 Hyttel. J. (1984) in 7th Symposium on Medicinal Chemistry (DahEbaum, R. and Nidsson, J. L. G., eds), pp. 42-39, Swedish Pha~a~utic~ Press Andersen, P. H. and Braestrup, C. (1986) J. Neumchent. 47,1822-1831 Andersen, P. H. et al. (1988) Sot. Neurusci. Abstr. 378.13 Mailman, R. 8. ef al. (1986) in Netrrobiology of Cenfraf D,-Receptors (Breese, G. R. and Creese, I., eds), pp. 5X72, Plenum Press 7 Dawson, T. M., Gehfert, D. R., McCabe, R. I’., Barnett, A. and Wamsley, J. K. (1986) J. Neurosci. 6, 2352-2365 8 Walaas, S. I. and Greengard, P. (1984) J. Neurosci. 4,84-98 9 Johansen, P. A. and White, F. J. (1988) Sot. Neurosci. Abstr. 377.7 10 Waddington, J. L., O’Boyle, K. M. and Murray, A. M. (1988) Ne~~mche~. I&. 13, F326 11 Amt, J., Hytfel, J. and Meier, E. (1988) Eur. J. Pharmacol. 155,37-46 12 Cameron, D. L. and Cmcker, A. D. (1988) Neurosci. Left. 90, 165171 13 Monsma, F. J., Burch, R. H., Sibley, D. R. and Mahan, L. C. (1989) Sot. Neurosci. Abstr. 171.9 14 DeCamiUi, I’., Macroni, 0. and Spada, D. (1979) Nature 278,252-254 15 Kelley, E. and Nahomki, S. R. (1987) Naunyn-Schmiedeberg’s Arch. Pharmacol. 335, 508-512 16 Freedman, J. E. and Weight, F. F. (1988) Proc. Nat1 Acad. 5n‘. USA 85, 3618-3622 17 Israel, M. M., Jaquet, P. and Vincent, J. D. (1985) E~~acr~nof~~ 117,1446-1455 18 Canonico, P. L., Valdenego, C. A. and Macleod, R. M. (1983) Endocrinology 113. 7-14 19 Vallar, L., Vicentini, L. M. and Meldolesi, J. (1988) J. Biol. Ckem. 263, lOl27-10134 20 Bockaert, J., Joumot. L. and Enjalbert, A. (1988) J. Recegt. Res. 8‘225-243 21 Wolf, M. E. and Roth, R. H. (1987) in Dupamine Receptors (Geese, I. and Fraser, C. M., eds). pp. 4%96, A. R. Liss 22 Clark, D., Hjorth, S. and Carlsson, A. (1985) J. Neural Tmasm. 62, l-5.: 23 Skirboll, L. R., Grace, A. A. and Bunney, B. S. (1979) Science 296,8@-82 24 Starke, K., Spath, L., Lang, J. D. and Adelung, C. (1983) Naunyn-Schmjedeberg’s Arch. Pha~aco~. 323,298-306 25 Clark, D., Hjorih, S. and C&sson, A. (1985) J. Neural Transm. 62,171-207 26 Meller, E., Bohmaker, K., Namba, Y., Friedhoff, A. J. and Goldstein, M. (1987) Mol. Pharmacol. 31,592-598 27 Herdon, H. (1988) Eur. 1. Pkarmacol. 15% x5-:16
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Pharmacol.
ADTN: dipropylaminotetraline NOll2: R(f)-8-chloro-7-hydroxy-3methyl-5-(7-benzofuran)-2,3,4,5-tetra hydra-lHJ-benzapine N0756: R(f)-8-chloro-7-hydroxy-3methyl-5-[7-(2,3-dihydro)benzofuran] 2~,4,S-te~ahydro-lH-3-benzapine .%X233% 7-~loro-2,3,4,5-te~ahydro-3me~yl-5-phenyl-lH-3-benza~epine-7-ol SKF38393: 2,3,4,5-tetrahydro-7,8dihydroxy-l-phenyl-lH-3-benzazepine SKF75670: 2,3,4,5-tetrahydro-3-methyl-7,8dihydroxy-l-phenyl-lH-3-benzazepine SKF77434: 2,3,4,5-tetrahpdro-3-al!yl-7.8dihydroxy-l-phenyl-lH-3-benzazepine
work; however, roots are evident in Magnus’s laboratory: there, in 1923 a remarkable little textbook* (Fig. 1) on pharmacology, ahead of its time, was written by W. Storm van Leeuwen (1882-1933). His career was unconventional for a scientist: after early retirement as a cavalry officer he studied medicine, he came to work with Magnus and in 1920 became professor of pharmacology in Leiden. His interest P~zu~a~~o~ is an active sport in the ~et~erlan~. Each of the country’s shifted to the immunological aseight universities has a depa~en~ o~pha~u~~lo~ and there are at least pects of allergy. When the universix government-operafed research institutes. This activity owes a debt to sity board rejected his request for the long history of the discipline. Rather than cataloguing today’sresearch hospital beds at the university or providing a rigid historical study, Erik Noach presents a pharmacolhospital, he founded his own ogist’s perspectiveon the sources and directions of pharmacological private clinic for allergic diseases, research in the ~e~her~an~. which attracted many - mostly foreign - patients. The good citizens of Leiden respectfully ALTHOUGH PHARMACOLOGY did not develop as a distinct watched the awkward high strucdiscipline until the early years of this century, there were several tures near the clinic where ‘undrug investigators working in the Netherlands before that time. polluted’ (by pollen) air was taken Among them were the internist B. J. Stokvis (1834-1902), professor in and filtered for the ‘allergenin Amsterdam, who wrote a textbook of materia medical (Fig. 1) free’ patient rooms. After his eariy which is still fascinating: to read, and C. A. Pekelha~g (l&%8- death in 1933 allergology was con1922) in Utrecht, who wai origtinued by clinical investigators. Heidelberg, was mainly interested inally a physiological chemist Magnus’s successor was his in direct effects of drug molecules but also worked on anatomy, pupil U. G. Bijlsma (1892-1977). In on organ functions. Hence, experhistology, general pathology addition to his own cardiovasiments with isolated preparations and pharmacology. were methodologically of prime cular investigations, he mainHowever, experimental pharmatained relations with the pharmaimportance; the ‘Magnus apparcology flowered with the appointatus‘ for in-vitro studies of smooth ceutical firm of Brocades (today, ments as professors of pharmamuscle preparations is still in use. after mergers, Gist-Brocades). cology of Rudolph Magnus (1873This ultimately led to the estabHis successors evolved this ap1927) in 1908 in Utrecht, and Ernst lishment of a pharmacochemistry proach to research on drugLaqueur (1880-1947) in 1920 in department there, led by W. Th. receptor interactions, structureAmsterdam. Their heritage can be Nauta, who later founded a simiactivity relationships and drug traced in Dutch pha~acolo~ up design. lar laboratory at the (P~testant) Magnus’s ‘scientific to the present day. Both came Free University in Amsterdam. He grandson’ E. J. AriiZns and the from Germany, but they had few latter’s co-workers - especially J. was succeeded by the present incommon scientific interests. M. van Rossum and A. M. Simonis cumbent H. Timmerman. The - made fundamental contributions ‘receptorologist’ J. Zaagsma in The influence of Magnus to this area. It is commonly asGroningen is another of Nauta’s Magnus (Fig. 2), who had worked sumed that ArKns’s studies are disciples although he was also in R. Gottlieb‘s laboratory in mainly inspired by A. J. Clark’s strongly influenced by Ariens.
