P.Soares-da-Silva, Dept. of Pharmacology and Therapeutics, Faculty of Medicine, 4200 Porto Portugal

Renal tubular epithelial cells are endowed with an enormous capacity to decarboxylate L-DOPA into dopamine; Nat and mechanisms involved in the tubular transport of Nag have been shown to be determinant factors in the control of tubular synthesis of dopamine (Soares-da-Silva & Fernandes, 1990, 1991). The, ultimate mechanism intervening in the process of Nae transport across epithelial cells of proximal tubules is that governed by Nag -Ke ATPase. This enzyme is localized at the basolateral membrane of tubular epithelial cells and the association between the actin cytoskeleton and Nat -K+ ATPase is determinant for the vectorial transport of Na (Molitoris, 1991). The aim of the present study is to determine the effects of inhibition of Nae -Ke ATPase activity by ouabain and inhibition of actin cytoskeleton by cytochalasin B on the synthesis of dopamine in rat kidney slices loaded with L-DOPA. The deamination of newly-formed dopamine into 3,4-dihydroxyphenylacetic acid (DOPAC) was also examined; tissue levels of dopamine and DOPAC were determined by high pressure liquid chromatography with electrochemical detection. Slices of rat renal cortex were preincubated for 30 min in warmed (37-C) and gassed (95% 02 and 5% CO2 ) and incubated for further 15 min with increasing concentrations of L-DOPA (10-100 pM). The formation of dopamine from L-DOPA in the presence of 120 mM NaC1 in the medium was found to be twice that in the presence of 20 mM NaCl; the osmolarity of the medium was kept constant by the addition of choline chloride. In experiments performed in the presence of 120 mM NaC1, but not in conditions of low Na4 (20 mM NaC1 in the medium), ouabain (100 and 500 pM) was found to inhibit the accumulation of newly-formed dopamine and DOPAC (14-57% reduction); this effect was more marked at 50 and 100 AM L-DOPA. Petreatment of rat renal slices with cytochalasin B (5, 10 and 50 jiM) resulted in a concentration-dependent reduction in the accumulation of dopamine and DOPAC (10-49% reduction). The inhibitory effect of cytochalasin B on the formation of dopamine was no longer observed in kidney slices incubated simultaneously with ouabain (100 jAM) or in conditions of low Nae (20 mM NaC1 in the medium). These results show that the renal formation of dopamine is dependent on the concentration of Na in the medium and on the integrity of a tubular transport system for Na , namely on the association between actin cytoskeleton and Nae -K4 ATPase. Molitoris, B.A. (1991). Am.J.Physiol., 260,F769-F778. Soares-da-Silva, P. & Fernandes, M.H. (1990) Am.J.Hypertens., 3,7S-10S. Soares-da-Silva, P. & Fernandes, M.H. (1990) Br.J.Pharmacol., 103,1923-1927.

Supported by a grant from the INIC (FmP1).



J.W. Dalley & R.A. Webster, Department of Pharmacology, University College London, Gower St, London WClE 6BT. Neuroleptic (NL) drugs probably act mainly by antagonising dopamine (DA). It is believed that atypical NLs, such as clozapine (CLZ), which give rise to fewer adverse motor disorders, may have less influence on the nigrostriatal DA system compared to typical NLs such as haloperidol (HAL) whilst remaining effective on mesolimbic and/or mesocortical DA systems.We have therefore compared the effects of CLZ and HAL alone both on the spontaneous efflux of DA and its metabolites (DOPAC and HVA) in the caudate nucleus (CP) and medial prefrontal cortex (MPFC) as well as on the effects of the DA agonist apomorphine(APO) in both areas. Spague-Dawley rats (250-300g) were anaesthetised with halothane and intracerebral dialysis probes inserted into either the rostral CP (A+1.5-2.0, L2.5-3.0, V7 mm relative to bregma) or MPFC (A+2.5-3.0, L0.4-0.9, V5.5) and perfused with artificial CSF (mMXNae 147, Ca2+ 2.30, K+ 4.00, Cl- 155.6, pH 6.5) at 5gl/min. Perfusates were collected every 20 mins and analysed for DA, DOPAC and HVA using HPLC with electrochemical detection. The effects of clinically equivalent doses of CLZ (20 mg/kg) or HAL (0.5 mg/kg) were monitored for 4 hours after their i.p. administration. APO was administered in increasing doses (0.025, 0.05, 0.1, 0.2, 0.5, 1.0, 2.0, 5.0 and 10 mg/kg i.v.) at 40 min time intervals either alone or after NL pretreatment. The maximum percentage changes in basal efflux (mean ± s.e. mean n=5) to APO (lmg/kg i.v.) before and after each NL and to each NL alone are given in Table 1. CP MPFC Table 1 DOPAC HVA DA DA EWPCHYA +59.0±11.2* +115.2±21.2* +23.3±6.2* +156.0±16.9* +116.3±7.8* CLZ 2omg/kg +4.8±1.2 +4.5±3.2 +142.2±30.7* +174.1±23.5* HAL 0.5mg/kg +3.9±1.9 +50.8±12.7* +90.2±7.3* -23.2±2.7* -72.7±l3.1* -59.5±12.8* -65.5±7.1* -53.5±5.0* APO lmg/kg -33.7±5.2* -30.1±6.3 -55.8±2.1# CLZ & APO -12.5±8.1# +8.7±6.9t +32.5±11.lt -13.1±2.4t -11.4±4.4# HAL & APO +72.2±8.2t +120.5±16.9t -0.9±4.8t +21.4±6.1t +41.8±5.3t * p guanabenz (IC50=21nM). In addition UK14304, amiloride, clonidine and guanethidine were found to be relatively potent each with IC50 values < lOjM. The a-adrenoceptor ligands RX821002, prazosin, adrenaline and noradrenaline were also tested and found to be inactive (IC50 values > 10-5M). None of the potassium channel openers tested (BRL38227, RP52891, P1060 and diazoxide) with the exception of pinacidil (ICso=4. IgM) had any effect on the binding of [3H] idazoxan. All agents identified as potent NAIBS ligands were inactive at displacing [3H] glibenclamide from the rat brain homogenate. The rat liver NAIB site is sensitive to imidazoline/guanidine type ligands but is unaffected by all but one of the potassium channel modulators. The ability of pinacidil to displace idazoxan binding may be attributable to the guanidine moiety within its structure and not to any potassium channel modulating properties. The lack of effect of any other potassium channel opener coupled with the inability of the NAIBS ligands to displace [3H] glibenclamide binding suggests that if the NAIB site is associated with a potassium channel it is unlikely to be blocked by glibenclamide or opened by agents like BRL38227. TI was supported by an MRC collarborative studentship in conjunction with Pfizer Central Research. Michel,M.C. and Insel,P.A. (1989) Trends Pharmacol Sci.,10, 342-344 Zonnenschein,R., Diamant,S. and Atlas,D. (1990) Eur J Pharmacol.,190, 203-215 K,


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T.V. Murphy', S. Foucart' & H. Majewski2, Department of Physiology and Pharmacology, University of Southampton, Southampton, S09 3TU, 'Department of Pharmacological and Physiological Sciences, University of Chicago, 947 East 58th Street, Chicago II. 60639, U.S.A. and 2Prince Henry's Institute of Medical Research, 68 Wells Street, South Melbourne 3205, Australia

cv2-Adrenoceptors function through GTP-binding proteins (G-proteins; Harrison et al, 1991). Prejunctional a2-adrenoceptors on sympathetic nerves inhibit noradrenaline release, however the identity of the G-protein involved in signal transduction of prejunctional a,-adrenoceptors is unclear. In a previous study, pertussis toxin, which inactivates the G-proteins Gi and G., did not alter the effects of cr2-adrenoceptor ligands on noradrenaline release from mouse atria (Musgrave et al., 1987). The aim of the present study was to further investigate the G-proteins involved in prejunctional a2-adrenoceptor signal transduction in mouse atria. Mouse atria were incubated with [jH]noradrenaline and then subjected to electrical field stimulation (5, 2.5, 1.75 Hz, 30 mA, 0.1 Ims, 60 s). The stimulation-induced outflow of radioactivity was taken as an index of endogenous noradrenaline release. At a stimulation frequency of 5 Hz, the a2-adrenoceptor agonist clonidine (0.03 ttM) inhibited noradrenaline release from the mouse atria by 29.5 %. This effect was not altered by pretreatment of the mice with pertussis toxin (1.5 jig). The a2-adrenoceptor antagonist idazoxan (0.1 MM) enhanced noradrenaline release from the mouse atria by 65.7 %, and this effect was also not altered by pertussis toxin. The possibility that the ineffectiveness of pertussis toxin was due to the presence of spare prejunctional a2adrenoceptors was investigated using St 363, an a2-adrenoceptor agonist of lower efficacy than clonidine (Medgett and McCulloch, 1980). At a stimulation frequency of 2.5 Hz, St 363 (10 gM) inhibited noradrenaline release from mouse atria by 27.2 %, and this effect was unaltered by pertussis toxin.

Following incubation of the mouse atria with another, less selective G-protein inactivator, N-ethylmaleimide (NEM; 3 MM, 60 min), neither clonidine nor St 363 inhibited noradrenaline release from this tissue. The facilitatory effect of idazoxan on noradrenaline release was reduced by approximately 80 % in atria incubated with NEM. These results suggest that prejunctional a,2-adrenoceptors on sympathetic nerves in mouse atria function through G-proteins which are sensitive to N-ethylmaleimide, but not pertussis toxin. The identity of these G-proteins remains to be elucidated. Harrison, J.K., Pearson, W.R. & Lynch, K.R. (1991) Trends Pharmacol. Sci., 12, 62-67. Musgrave, I.F., Marley, P. & Majewski, H. (1987) Naunyn-Schmiedeb. Arch. Pharmacol., 339, 48-53. Medgett, I.C. & McCulloch, M.W. (1980) J. Pharm. Pharmacol., 32, 137-138.


CHRONIC Pl-ADRENOCEPTOR ANTAGONIST TREATMENT DOES NOT AFFECT ACTIVITY OF GS-PROTEIN OR ADENYLATE CYCLASE IN HUMAN RIGHT ATRIUM M.C. Michel, A. Broede, M. Michel-Reher, H.-R. Zerkowski & O.-E. Brodde, Dept. Medicine, University of Essen, Hufelandstr. 55, D-4300 Essen, Germany It has previously been demonstrated that B12-adrenoceptor-mediated positive inotropic effects are enhanced in atria of patients chronically receiving 81-selective antagonists although no increases of B2-adrenoceptor density were detected (Hall et al. 1990, Motomura et al. 1990). We have now studied whether alterations distal to the B2-adrenoceptor such as G-proteins or

the catalytic subunit of adenylate cyclase may be involved in this sensitization.

Right atria were obtained from patients without apparent heart failure undergoing coronary artery bypass grafting which had or had not been treated with Bl-selective adrenoceptor antagonists (atenolol, metoprolol, bisoprolol) for at least 3 weeks prior to surgery. Adenylate cyclase was assessed in atrial membranes as conversion of [32P]ATP to [32P]cAMP during a 10 min incubation at 30 . G8 function was assessed as 10 mM NaF-stimulated adenylate cyclase activity following reconstitution of four concentrations of atrial membrane extracts into cyccell membranes. The a-subunits of the G-protein G, and G1112 were quantified by quantitative Western blotting with the specific RM/1 and AS/7 antisera, respectively, followed by [125I]_ protein A detection. G10 was also quantified using pertussis toxin-catalyzed ADP-ribosylation. At least 8 patients were studied in each group. Adenylate cyclase stimulation by GTP (100 MM) or NaF (10 mM), which directly activate G-proteins, and by forskolin (10 MM) or MnCl2 (10 mM), which directly activate adenylate cyclase, was not significantly different between B1-antagonist-treated and control patients. We also failed to detect significant differences between the two groups for reconstituted G. activity, immunodetectable G. and Gi0 or pertussis toxin substrates (1213±178 control and 980±145 fmol/mg protein BL-antagonist-treated patients). We conclude that altered amounts of G, or G1Q or changes in the functional activity of G, or the catalytic subunit of adenylate cyclase may not contribute to the enhanced 32-adrenoceptor function in atria from patients chronically receiving B3-adrenoceptor antagonist treatment.

Hall, J.R., Kaumann, A.J. & Brown M.J. (1990) Circ. Res. 66, 1610-1623. Motomura, S., Deighton, N.M., Zerkowski, H.-R., Doetsch, N., Michel, M.C. & Brodde, O.-E. (1990) Br. J. Pharmacol. 101, 363-369.



EXPOSURE TO AGONIST A.B. Tobin , D.G. Lambert and S.R. Nahorski, Department of Pharmacology and Therapeutics, University of Leicester, P.O. Box 138, Medical Sciences Building, University Road, LEICESTER. LE1 9HN. U.K.

Of the five cloned muscarinic receptor subtypes three (ml, m3 and m5) are coupled efficiently to the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP ). Previous studies have demonstrated that desensitisation of ml and m3 muscarinic receptor mediated responses following prolonged (>2hr) agonist exposure are associated with receptor sequestration and/or down regulation (1). However, muscarinic receptors coupled to PIP2 hydrolysis appear to be relatively insensitive to desensitisation following short exposures to agonist. In this study we describe desensitisation of m3 muscarinic receptor mediated responses following a short 5 min pre-exposure to agonist. The effect of carbachol on inositol 1,4,5-trisphosphate (InsP ) levels in Chinese Hamster Ovary cells expressing transfected m3 muscarinic receptors (Bmax = 2384 fmol/mg protein, Kd = 0.157nM for [3 HIN-methyl scopolamine) was monitored using an InsP3 mass assay. Application of 1mM carbachol results in a rapid increase in InsP3 rising to an initial peak 6.82 + 0.36 fold over basal (± SE, n=3) within 10 secs. In the following 50 secs InsP fell to 4.09 + 0.18 fold (n=3) over basal, a level which is maintained for at least 5 min and which constitutes the plateau phase of the response. A 5 min pre-exposure to 1mM carbachol followed by a 2 min wash eliminates the peak InsP3 response of a subsequent agonist application without affecting the later plateau phase. This effect is reversible with the complete recovery of the carbachol response occurring within 15 min of the desensitising pulse of agonist. Since the primary function of InsP is to mobilise intracellular stores of calcium the anticipated cellular consequence of desensitisation of the InsP, peak would be a reduction in agonist-mediated calcium mobilisation. This was investigated using the calcium chelating fluorophore FURA-2 in conjunction with standard epifluorescence microscopy. In control cells the application of 1mM carbachol results in a rapid peak of free intracellular Ca + (basal F34, /F 80 ratio = 0.74 + 0.05 and peak ratio = 2.72 + 0.22 (±SE, n=12) a response that correlates with the peak ot InsP3 3 production. Pre-exposure of the cells to ImM agonist for 5 minutes followed by a 2 min wash period reduced the Ca 2 + peak stimulated by a subsequent application of carbachol by >50%. As in the case of InsP3 mass desensitisation the Ca + response was completely restored within 15 min of the initial agonist exposure. This desensitisation phenomena cannot be accounted for by receptor sequestration or down regulation since no change in [ HIN-methyl-scopolamine binding is observed following a 5 min exposure to agonist. Other mechanisms of desensitisation, such as receptor uncoupling, are currently under consideration. 1.


Hu, J., Wang, S.-Z. & El-Fakahany, E. (1991) J. Pharm. Exp. Therap., 257, 938-945.


BOVINE TRACHEAL SMOOTH MUSCLE CELLS K.A.Marsh & S.J.Hill, Department of Physiology & Pharmacology, Medical School, Queen's Medical Centre, Nottingham, NG7 2UH. It is widely accepted that intracellular calcium ions are the primary regulators of smooth muscle contraction, an increase in which can be triggered by agonist-induced phospholipid hydrolysis. Bradykinin-B2 receptor stimulation has been shown to mediate smooth muscle contraction in several isolated tissues (Regoli et al, 1990). In this study we report the effects of bradykinin on phosphoinositide hydrolysis and calcium ion mobilisation in cultures of bovine tracheal smooth muscle cells. Cell cultures were prepared from fresh strips of bovine tracheal smooth muscle. Briefly tissue was chopped into lmm3 pieces which were then transferred to 75cm2 tissue culture flasks. 10ml of D-val MEM (Gibco) supplemented with 10% FCS was added to each explant culture which was then incubated at 37oC in a 10% CO2 humidified atmosphere. A complete change of media was performed every 3.4 days until confluency when explants were discarded. Cells were subcultured using a 0.05% trypsin/EDTA solution. All experiments were performed on cells between passage 3 and 9. Identification of smooth muscle cells was confirmed by indirect immunocytochemistry using a monoclonal antibody to alpha smooth muscle actin. Cell monolayers grown in 24-well plates were loaded with 3H-myo-inositol (lItCi/well) for 72 hr in inositol-free DMEM supplemented with 0.5% FCS and 2mM glutamine. Cells were then washed twice with lml Hanks/HEPES buffer, pH7.4 and incubated for 30 min in 0.7ml Hanks/HEPES with 20mM LiCI. Where appropriate antagonists were added after 28 min incubation. Agonists were added in 1011 of medium for incubation times of 2.5 to 45 min. Stimulation was stopped by the addition of lml ice cold methanol/0. 12ml HCI (1:1 v/v). Cells were left overnight at -20OC before total inositol phosphates in the supematant were separated by anion-exchange chromatography (Hall & Hill, 1988). For image analysis, cells were sparsely seeded and grown for 48 hr on 22mm circular glass coverslips. These were then loaded with 5gM Fura-2 AM and placed in a holder with 900j1 of physiological salt solution containing 2mM CaCl2 and maintained at 37oC by means of a heated chamber. Agents were added in a volume of 100pl directly onto the coverslip and changes in calcium ion concentration within single cells were monitored using a Nikon fluorescent microscope and the Joyce Loebl Magical image analysis system. Bradykinin (0.1j±M) produced an increase in 3H-inositol phosphate accumulation which was evident after 2.5 min and began to plateau between 25 and 45 min after agonist stimulation. The response to bradykinin (0.1AkM) increased with increasing concentrations of LiCl (up to 50 mM) in the preincubation solution. Concentration response analysis of the bradykinin response revealed a log EC50 (M) of -9.43 ± 0.20 (n=8) at 10 min incubation and an Em.. of 5.53 ± 0.99 fold over basal levels. The bradykinin B -receptor agonist, Des-Arg9-bradykinin was without significant effect on inositol phosphate accumulation at concentrations up to 101M. The bradykinin-B, receptor antagonist Des-Arg9 -[Leu8]-bradykinin showed no antagonism of the bradykinin response. However, the bradykinin-B2 receptor antagonists D-Arg-Hyp3-D-Phe7-bradykinin (KD = 40 ±14 nM n=3) and D-Arg-Hyp3,Thi5.8-D-Phe-bradykinin (KD = 8.58 ± 2.80 nM; n=3) both produced parallel shifts of the bradykinin dose-response curve to higher agonist concentrations indicating competitive antagonism at bradykinin-B2 receptors. Bradykinin (InM - l0pM) produced a partially sustained increase in intracellular calcium ion concentration [Ca2+]i in 80% of the bovine tracheal smooth muscle cells studied in Ca2+-containing buffer (n=45). In Ca2+ -free buffer 67% of cells responded to bradykinin at a concentration of lOnM (n=6). The addition of forskolin (l0OgM), a known activator of adenylate cyclase was able to return the increased [Ca2+1j, in response to bradykinin (InM), to a basal level in calcium-containing buffer. These results indicate that cultured bovine tracheal smooth muscle cells are a useful tool in the investigation of the control of phospholipid hydrolysis and calcium mobilisation by bradykinin-B2 receptors in airway smooth muscle. We would like to thank the AFRC for their financial support of this work. Hall, I.P. & Hill, S.J. (1988) Br. J. Pharmacol. 95, 1204-1212. Regoli, d., Rhaleb, N.E., Dion, S. & Drapeau, G. (1990) Trends Pharmacol. Sci. 11, 156-161.


DDTlMF-2 John M. Dickenson & Stephen J. Hill. Department of Physiology and Pharmacology, Medical School, Queen's Medical Centre, Nottingham, NG7 2UH. Agonist induced Ca2+ influx into cells can occur by at least two mechanisms: one controlled by the Ca2+ content of the intracellular store and one which is dependent upon continued receptor activation (Meldolesi et aL, 1991). In DDT1MF-2 cells, histamine HI-receptor activation can stimulate a release of intracellular Ca2+ and an influx of extracellular Ca2+ (Dickenson & Hill, 1991). In this study, we have investigated the nature of the histamine (HA) stimulated Ca2+ influx in DDT1MF-2 cells.

Monolayers of DDT1MF-2, were grown on glass coverslips and loaded with fura-2/AM. [Ca2+1, changes elicited by HA stimulation were then measured essentially as described previously (Dickenson & Hill, 1991). Stimulation with HA (100 PM: EC50 7.9 x 10-6M ± 0.2, n=4) in Ca2+-free medium (containing 0. 1mM EGTA) caused a rapid and transient rise in ICa2+],. The subsequent readdition of exogenous Ca2+ (2mM) resulted in a further increase in ICa2+11 which appeared to be due to Ca2+ influx (N=5). Addition of mepyramine (10 pM; N=3), applied 8 min prior to 2mM CaCI2, attenuated the rise in ICa2+li observed when Ca2+ was reapplied. Pretreatment with Ni2+ (1mM; N=3) or C02+ (1mM; N=3) inhibited the Ca2+ influx, whereas, the organic voltage-operated Ca2+ channel antagonists nifedipine (10 pM; N=3) and PN-200-110 (10 pM; N=3) were without effect. After stimulation with HA (100 pM) in Ca2+-free medium, the response to a subsequent addition of bradykinin (BK; lOOnM) was markedly reduced. However, if exogenous Ca2+ (2mM) was applied for a short period (5 min, in the presence or absence of 10 pM mepyramine) between the HA and BK stimuli, a maximal BK response was re-established (n=5). Furthermore, during this refilling of the internal Ca2+ stores in the presence of mepyramnlne, there was no observable rise in ICa2+i1. The results of this study suggest that HI-receptor activation in DDT1MF-2 cells stimulates both release of Ca2+ from internal stores and Ca2+ influx which may be through a receptor-activated Ca2+ channel. Furthermore, the subsequent refilling of the internal Ca2+ store appears to be independent of HI-receptor activation and can occur without a noticeable rise in cytosolic free


We thank the Wellcome Trust for financial support.

Dickenson, J.M. & Hill, S.J. (1991) Blochem. PharmacoL 42, 1545-1550 Meldolesi, J., Clementi, E., Fasolato, C., Zacchetti, D. & Porzan, T. (1991) Trends PhanracoL Sct 12, 289-292



D.R. Tomlinson & C.B. Ettlinger, Department of Pharmacology, Queen Mary and Westfield College, Mile End Road, London El 4NS, U.K.

Circumstantial evidence has linked myo-inositol metabolism to basal activity of ouabain-sensitive ATPase in sciatic nerve homogenates and phosphoinositide-derived kinase activation has been suggested as the link (Simmons et al. 1982). We have therefore examined the capacity of activators and inhibitors of protein kinase C (PKC) to modulate activity of the sodium pump in cells of the endoneurium of the rat sciatic nerve. These preparations are made by desheathing the nerve and then fenestrating the perineurium of the major fascicle by microdissection. Activity of the sodium pump was measured as ouabain-sensitive uptake of rRb] in preparations incubated in Krebs-Henseleit bicarbonate-buffered saline, containing 3% defatted bovine serum albumin, at 37C equilibrated with 95%02/5%CO2 over a 30 min period, during which uptake was linear without intervention. Permeation of extracellular space was monitored by inclusion of [3H] sucrose in the incubate. Uptake was therefore calculated with reference to nerve protein and [3H] content and is expressed below as % basal activity, derived from control preparations, ± 1 SD, with significance values calculated by one-way ANOVA with Duncan's multiple range tests. Preparations were incubated either in the presence (ouabain-resistant uptake) or absence (total uptake) of 2 mM ouabain and the ouabain-sensitive activity (Na+/K' pumping) inferred by subtraction. Total ["ORb] uptake was increased by 47±14% (p 10000 144 ± 25 (3) 148 ± 19 (3)


U373MG 0.49 ± 0.08 (4) 39.8 ± 1.3 (4) 3214 ± 679 (3) 0.8 ± 0.1 (3) 6.2 ± 0.8 (3)

OCH3 || t 0 Figure 1: Structure of RP 67580 In all binding assays, a clear stereoselective action is found between RP 67580 and its enantiomer RP 68651. In rat and mouse, RP 67580 inhibits [6H]SP binding with high affinity in comparison to the quinuclidine compounds. Saturation studies pegformed in rat brain membranes,with or without RP 67580, show that this compound is a competitive inhibitor of [ HJSP binding. Although less marked than with CP-96,345, reverse species variation in affinity is observed with RP 67580 and the order of potency of antagonists differed in U373MG, in comparison to rat and mouse. In addition, RP 67580 displays high selectivity for the SP receptor, since it does not ighibit, at concentrations up to 10 FM, the binding of [3Hjpropionyl-NWA to rat duodenum (NW2 sites), nor that of [ Hlsenktide to guinea-pig cortex homogenates (NK3 sites). It does not displace binding to any other receptors studied. In conclusion, RP 67580 appears to be the most potent SP antagonist described so far in rat and mouse. It should be a powerful tool for the investigation of the roles of SP in physiology and pathology, since it has strong SP antagonist activity in rodents and human cell lines (this meeting). In addition, the relative affinities of both RP 67580 and CP-96,345 should be very useful to further characterize tachykinin receptors.

Garret,C., Carruette,A., Fardin,V., Moussaoui,S., Peyronel,J.F., Blanchard,J.C. & Laduron,P.M. (in press) Proc. Natl. Acad. Sci. (USA). Snider,R.M., Constantine,J.W., LoweIII,J.A., Longo,K.P., Lebel,W.S., Woody,H.A., Drozda,S.E., Desai,M.C., Vinick, F.J., Spencer,R.W. & Hess,H. (1991) Science 251, 435-437.

Proceedings of the British Pharmacological Society Meeting. London, 17-19 December 1991. Abstracts.

1P ROLE OF ACTIN CYTOSKELETON IN THE REGULATION OF THE RENAL SYNTHESIS OF DOPAMINE P.Soares-da-Silva, Dept. of Pharmacology and Therapeutics, Facult...
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