Regulation of ion transport across gallbladder epithelium.

ANNUAL REVIEWS

h9

1991. 53:361-73

Further

Quick links to online content

Annu. Rev. Phvsiol. Copyright © I by Annual Reviews Inc. All rights reserved

Annu. Rev. Physiol. 1991.53:361-373. Downloaded from www.annualreviews.org Access provided by Technische Universiteit Eindhoven on 02/01/15. For personal use only.

REGULATION OF ION TRANSPORT ACROSS GALLBLADDER EPITHELIUM

Luis Reuss, Yoav Segal, and Guillermo Altenberg Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston, Texas 77550 KEY WORDS:

fluid absorption, sodium transport, potassium transport, chloride transport

INTRODUCTION

Overview Many of the transport mechanisms accounting for baseline salt transport in gallbladder epithelium have been characterized (37). Recent studies have focused on the means by which transport is regulated. The rate of transepithe lial ion absorption is the result of the integrated activity of transporters in the cell membranes. Short- and/or long-term modulation of the activity of specific transporters can involve multiple factors andlor mechanisms, including mem brane voltage, membrane stretch, effects of ions (e.g. H+, Ca2+) at mod ulatory sites, covalent modification (e.g. phosphorylation, methylation), di rect modulation by regulatory proteins, and alterations in the surface density of transporting units. In epithelia, there is also the need for steady-state adjustment of the transport rates at both cell membrane domains if cell volume and composition are to be preserved when the rate of transepithelial transport is altered (46). In gallbladder epithelium, the best understood regulatory mechanisms in361

0066-4278/91/0315-0361$02.00

362

REUSS, SEGAL & ALTENBERG

volve intracellular factors such as pHi, Ca2+i' and cyclic AMP (cAMP). Changes in intracellular levels of these and other agents mediate the effects of hormones and neurotransmitters on salt transport (see below). Our discussion will center on the effects of intracellular second messengers. In this review, we summarize information on the regulation of specific transporters and discuss means by which regulation is integrated to eventually determine the overall rate of fluid transport. Historically gallbladder epithe


lium has served as a model for leaky epithelia. To the extent that there are parallels between transport regulation in gallbladder and in epithelia of greater homeostatic significance, such as the renal proximal tubule and the small intestine, studies on the former may enhance our understanding of the com plicated means of maintenance of body fluid volume and composition. Per turbations such as large changes in HC03 -/C02 are unlikely to play a regulatory role in vivo, but will be discussed because their study can help understand the mechanisms by which other permeant buffers modulate salt

transport (23).

There are significant differences in transepithelial transport processes in gallbladders of different species. While acknowledging these complications,

we will focus our review on results obtained in the gallbladder of Necturus

maculosus because ion transport mechanisms at the cell membrane level have been characterized extensively in this species.

Ion Transport in Gallbladder Epithelium The main transport function of the gallbladder is the absorption of NaCI and water in near-isosmotic proportions (10). This involves apical membrane entry of Na+ and Cl- and basolateral membrane extrusion of both ions. The Na + and Cl- influxes across the apical membrane are via parallel, in dependent Na+/H+ and Cl-/HC03 - exchangers (35, 41, 60, 61, 65), although it is possible that there is also NaCI or NaKCI cotransport (8, 9, 24). Although quantitatively less important than NaCl absorption, the gallbladder epithelium also secretes K+ and H+ (10, 18, 33). In addition, in some mammalian species (e.g. the guinea pig) HC03- is secreted instead of

absorbed (62). Basolateral membrane Na+ exit is mediated by the (Na+ ,K+)

activated ATPase, and CI- extrusion appears to result from both conductive

transport (52, 55) and electroneutral KC1 cotransport (5, 34). Both cell

membranes are K+ selective. Single K+ channels originating from apical or basolateral membranes have been recently studied with the patch-clamp technique (see below). The mechanisms of transepithelial transport in gallbladder have been re

viewed (37-39, 45, 50) and are summarized for the case of Necturus gallblad der epithelium in Figure 1.


ION TRANSPORT IN GALLBLADDER

HCO

363

�""r"'--

3 .... 4��

-

_

H+"'�:---

Apical �I::)a-,,� Membrane

Figure 1

\. Basolateral

�_____

Membrane

Transepithelial ion transport model for NeClurus gallbladder. Directions of fluxes

observed in steady state are depicted. Apical membrane NaCI entry is via parallel Na+/H+ and Cl-/HC03- exchangers. Basolateral Na+ extrusion is via the Na+ pump; Cl- exit is by KCl cotransport and a Cl- conductive pathway. There are K+ -selective channels in both membranes, but K+ recycles mostly at the basolateral border, which has a much higher K+ conductance. There is also some basolateral Na+ recycling. A small apical Na+ conductance is not shown (reproduced with permission of the American Physiological Society).

REGULATION OF APICAL MEMBRANE Na+ AND Cl TRANSPORT

Regulation of the Rate of Apical Membrane Na + IH+ Exchange EFFECT OF pHo

In tissues bathed in a medium containing 110 mM [Na+]o

and buffered with HEPES, reductions of mucosal solution pH cause decreases in intracellular Na + activity (aNai), which suggests that external pH (pHo) can

modify Na+ entry and salt absorption under physiologic conditions (1). The relationship between pHo and the rate of fall in aNai is compatible with

titration of a single site with an apparent pK of 6.3.

The apparent Km of the Na+ /H+ exchanger for mucosal Na+, determined from apical Na+ entry and mucosal solution acidification, is about

15 mM (1,

364



60); kinetic analysis of apical membrane Na+ entry at pHo 7. S and 6. S showed that external acidification raises the apparent Krn for Na+ to =130 mM without change in apparent Vrnax (1). Thus the inhibition of Na+/H+ exchange by external H+ appears to be purely competitive. EFFECT OF pHi At resting pH;, the activity of the exchanger is about 30% of the maximal rate and can account for salt absorption under basal conditions (1). Consistent with this view, amiloride inhibits salt absorption and reduces aNai (35). The dependence of Na+/H+ exchange on pHj is steeper than the dependence on pRo and cannot b� explained by titration of a single site. The most likely explanation is allosteric modulation at a cytosolic site, as shown in other systems (2). These observations indicate that both pHo and pHi can, in principle, regulate salt absorption via changes in Na+/H+ exchanger activity, but pH; would have a greater effect because of the higher apparent pK of the internal site (7.1) and the steeper dependence of the Na+/H+ exchanger on pH; compared to pHo.

Elevating intracellular cAMP levels decreases the rate of fluid absorption by gallbladder epithelium (30) and in some species can elicit net secretion (62). A number of agents, including prostaglandins, secretin, vasoactive intestinal peptide (VIP), bradykinin, and vasopressin, elevate intracellular cAMP levels, which suggests that this mechanism is responsible for the effects of these agents on salt and water transport (28, 63). Maximal elevations of cAMP, elicited by phosphodiesterase inhibition (theophylline), adenylyl cyclase stimulation (forskolin), or exposure to the permeant cAMP analogue 8-Br-cAMP, reduce apical membrane Na+/H+ exchange in Necturus gallbladder by about 50% (44). An inhibitory effect of cAMP on H+ secretion has also been demonstrated in guinea pig gallbla dder (31). The conclusion of inhibition of Na+/H+ exchange by cAMP in Necturus gallbladder is based on the following observations: (a) reduction of aNa; upon elevation of intracellular cAMP levels, (b) decrease in the rate of fall of aNa; upon lowering mucosal solution [Na+], (c) inhibition of the pHi recovery from an acid load (the recovery is largely mediated by apical Na+/H+ exchange), and (d) reduction of mucosal solution acidification upon stopping mucosal superfusion. The inhibition of pH; recovery from an acid load by cAMP involves a reduction in apparent Vmax, without a change in apparent Km for external Na+ (44). EFFECT OF cAMP

Regulation of the Rate of Apical Membrane CZ-IHC03 - Exchange The dependence of CI-IHC03 - exchange on pHo and pHi has not been studied in detail in gallbladder, but experiments in lymphocytes and Vero cells (27. 29) have shown that CI-IHC03 - exchange

EFFECTS OF pHo AND pHi



365

is exquisitely sensitive to pHi. The steep increase of Cl-IHC03 - exchange upon increasing pHi in HEPES-buffered solutions suggests allosteric regula tion by pHi. The information available from Necturus gallbladder epithelium suggests that Cl-IHC03- exchange is affected by pHi. When Na+ is removed from the mucosal solution, the intracellular Cl- activity (aCID falls more slowly than aNaj, thus indicating that the coupling between Na+ and Cl entry through the apical membrane is indirect, probably via changes in pHi and/or [HC03-]i (35, 60). Amiloride inhibition of apical membrane Na+ IH+ exchange also causes cell acidification, a fall in aNaj, and a slower decrease of aClj (35, 60). The effect of intracellular HC03 on CI-IHC03- exchange is evident when gallbladders are incubated in HC03 -IC02 buffered solution instead of HEPES-Ringer (40). Regardless of the larger intracellular buffering power in tissues bathed in HC03-IC02 media, the intracellular alkalinization elicited by removing mucosal solution Cl- is increased, which indicates that the Cl-IHC03 - exchanger is more active in physiologic solutions with higher [HC03-]. The effect of pHo on Cl-IHC03- exchange seems to be of minor importance since apical membrane Cl- entry is not affected by pHo reductions of 1 unit, i.e. by decreasing HC03- from 10 to 1 ruM, provided that the sum of the chemical gradients for CI- and HC03- is kept constant by reducing simultaneously external [CI-] (36). -

Increases in intracellular cAMP levels produced by theo phyline forskolin, or 8-Br-cAMP, reduce CI-IHC03- exchange by about 50%, as demonstrated by a decrease in the rate of mucosal solution alkaliniza tion when the Na+lH+ exchanger is blocked, and by a decrease in the voltage-independent rates of fall in aClj and aHC03-j upon changing luminal solution [CI-] or [HC03-] (36). This effect results from the reduction of the apparent Vmax of the system without effect on the apparent Km for external Cl- (36).

EFFECT OF cAMP ,

Effect of cAMP on Apical Membrane Cl Conductance (gCe) Increases in cAMP produce cell membrane depolarization and a decrease of the ratio of apical to basolateral membranes resistances, Ra/Rb (30, 36, 44). The underlying mechanism of these effects is an increase in apical membrane gCI-, which is best evidenced by the large and rapid depolarization observed upon reducing mucosal solution CI-, an effect absent prior to cAMP treat ment (30). In Necturus gallbladder, the cAMP-induced apical membrane gCI- is insensitive to agents that block Cl- channels in other cells (41, 58), but can be reduced by a monoclonal antibody raised against Necturus gall bladder epithelial cells (11). The cAMP-induced fall in aClj is due to the combined effects of inhibition of Cl-IHC03- exchange and stimulation of gCI-.


366


Single Cl- channels likely to account for the cAMP-induced gCI- have been identified in gallbladder epithelial cells treated with theophylline or forskolin, but not in control tissues (47). More recently, monoclonal antibod ies raised against Necturus gallbladder epithelial cells have allowed for isolation of proteins that when incorporated in planar lipid bilayers exhibit channel activity (56). In guinea pig gallbladder, cAMP induces net secretion of both fluid and HC03 - . The latter effect is attributable to stimulation of CI-IHC03 - ex change, caused by the decrease in aClj, and enhanced conductive HC03 - eJi.:it (51). The possibility of a direct effect of cAMP on Cl-IHC03 - exchange has not been explored in this preparation. It was claimed that cAMP increases apical membrane HC03 - conductance in Necturus gallbladder epithelium (64), but later experiments appear to rule out this possibility (36, 37). REGULATION OF BASOLATERAL MEMBRANE Na + AND Cl- TRANSPORT

Regulation of the Rate of the Na+ Pump Direct studies of the mechanisms of regulation of the rate of the Na+ pump are lacking in gallbladder epithelium. It is clear, however, that changes in pump activity must occur in response to primary increases or decreases in the rate of Na+ entry, i.e. an elevation of Na+ entry is expected to stimulate the pump, and a reduction in Na+ entry would inhibit it (see below). An obvious mechanism that would explain the relationship between apical Na+ entry and basolateral Na+ extrusion is the change in aNaj elicited by alterations of apical entry. When Na+ transport is stimulated by incubation in HC03 -/C02 media or inhibited by cAMP, however, there are no changes in aNaj, or the changes are too small to account for the changes in pump activity predicted from the rate of fluid absorption. Hence, under these conditions it is likely that other factors influence the rate of active Na+ transport across the basolateral membrane. On the basis of studies in other tissues, possible mechanisms include changes in cell volume and intracellular pH.

Regulation of Basolateral Membrane Cl- Transport In low-HC03 - media the baso lateral membrane gCI- is small, about 6% of the basolateral conductance (32). Incubating the tissues in media buffered with HC03 -/C02 increases Ra and decreases Rb (52); the former effect results from a decrease in apical membrane electrodiffusive K+ permeability (PK) and the latter from increases in basolateral membrane PK and PC! (55). Consequently, in 10 mM

EFFECT OF PERMEANT BUFFERS ON gCl-


367

HC03 II % CO2 about 50% of the total conductance of the basolateral membrane is due to Cl- (55). -

Lowering pHo, by decreasing serosal solution [HC03-]0 at constant pC02 , or by increasing pC02 at constant [HC03-]0. increases basolateral gCI- and causes cell membrane depolarization (55). The depolarization occurs without measurable change in RalRb, which suggests that if permeability changes are restricted to the basolateral membrane, they must involve both an increase in PCI and a decrease in PK (55). Raising serosal solution pC02 and [HC03 -] (constant pHo) causes a fall in pHi without changes in basolateral membrane voltage. Thus basolateral membrane PC! appears to be insensitive to pHi changes, at least in the range of 7.4 to 7. 1 (55).


pH DEPENDENCE OF BASOLATERAL cl- CONDUCTANCE

REGULATION OF K+ CONDUCTIVE PATHWAYS

Regulation of Macroscopic K+ Conductances The apical and basolateral cell membranes in amphibian (42, 43, 57) and mammalian (20, 57) gallbladder are predominantly K+ -conductive. As a result, the K+ equilibrium potentials across these membranes determine both the cell membrane voltages and the electrical driving forces for ion transport. In Necturus and rabbit gallbladder, the apical membrane appears to provide a pathway for K+ secretion, which amounts to a small fraction of Na+ absorp tion (18, 33). The apical membrane of Necturus gallbladder epithelium constitutes 6090% of the total transcellular resistance under baseline conditions (52). In transepithelial current- and voltage-clamp studies, depolarization of the apical membrane decreases RaiRb' This effect is inhibited by adding the K+ channel blocker TEA+ to the mucosal bathing solution, which suggests that de polarization activates an apical membrane K+ conductance (14, 48, 53). The apical membrane of guinea pig gallbladder also contains a voltage-activated K+ conductance (17). In Necturus gallbladder, elevation of intracellular Ca2+ levels with Ca2 + ionophores enhances the effects of membrane depolariza tion, whereas lowering pHo decreases them. These observations imply that gK+ is increased by [Ca2 +h and decreased by external H+ (14). The basolateral membrane conductance of Necturus gallbladder appears to be voltage-insensitive, as assessed in transepithelial voltage-clamp studies (14). Elevation of intracellular Ca2+ levels with A23187 or cyanide leads to a rapid hyperpolarization of the cell membrane voltages and an increase in the K+ selectivity of the basolateral membrane (3), thus suggesting that K+ channels in this membrane can be activated by internal Ca2 +. As noted earlier, acidification of the serosal bathing solution is likely to lead to a

368


decrease in the absolute K+ conductance of the basolateral membrane, con comitant with an increase in gCI- . Evidence points to an external, rather than internal, modulatory site for H+ (55).


Regulation of K+ Channels Potassium channels were flrst demonstrated in gallbladder epithelium by fluctuation analysis (15, 16). More recently, the patch-clamp technique has made it possible to identify and to characterize in detail single ion channels that account for some properties of the macroscopic apical and basolateral conductances. In cell-attached patch-clamp experiments carried out on the apical mem brane of Triturus (26) and Necturus (48) gallbladders, the most commonly observed channel is a large-conductance ( 200 pS) maxi K+ channel, which is largely inactive (open probability < 0.15) at the resting membrane voltage, and activates steeply with depolarization of the membrane patch. In cell excised membrane patches, maxi K+ channels from Triturus and Necturus are activated by membrane depolarization, or elevation of internal Ca2 + levels, like their counterparts in excitable cells, in which channels of this type were characterized originally (see 25). In Necturus gallbladder, maxi K+ channels account for no more than 20% of the resting apical membrane conductance, assessed on the basis of the open probability at the resting membrane voltage, and simple models relating single-channel properties to the macroscopic conductance (48). Maxi K+ channels account for the voltage- and Ca2+ -sensitive components of apical membrane conductance, described above, and its pharmacological sensitivities (49). It is likely that these channels also participate in the overall response to cAMP, inasmuch as they would be activated by the depolarization elicited by this agent. For instance, the cAMP-induced reduction in cell volume (C. Cotton, L. Reuss, unpublished observations) could result in part from net KCl loss across the apical membrane. Apical membrane depolariza tion elicits K+ secretion because of the change in electrochemical driving force and because of gating of voltage-sensitive K+ channels. Although of minor importance in gallbladder, regulation of K+ secretion is a major function of other epithelia, such as the renal collecting tubule. Recent ex periments show that the open probability of maxi K+ channels from the apical membrane of Necturus gallbladder epithelial cells is decreased by reductions of pHi near the physiologic range (4). K+ channels underlying the resting apical membrane K+ conductance in gallbladder epithelium have yet to be identified. Obstacles to their identiflca tion could arise from (a) low single-channel conductance, (b) low frequency of transitions between open and closed states, and/or (c) a tendency to run-down under the conditions of patch-clamp experiments. Low-con-

ION TRANSPORT

IN

GALLBLADDER

369

ductance channels, which rarely close at the resting membrane voltage, have recently been described in several epithelia (e.g.

12).

Patch-clamp experiments on epithelial basolateral membranes are hindered

by the presence of subepithelial connective tissue layers. In Necturus gall

bladder, the recent development of a technique for exposing "clean" areas of basolateral membrane has permitted identification of several kinds of K+


channels that are not yet fully characterized

(59).

COORDINATED REGULATION OF APICAL AND BASOLATERAL MEMBRANE ION TRANSPORT In the steady state, changes in the rate of transepithelial transport must involve parallel alterations of the rates of salt entry across the apical membrane and salt extrusion across the basolateral membrane. These adaptive mechanisms prevent large changes in cell volume and/or ion content in response to primary stimulation or inhibition of transport at either membrane domain

(46). An

obvious mechanism linking the transport rates across the two membranes is the change of intracellular ion activity resulting from the primary event. For instance, inhibition of Na+JH+ exchange will cause a fall in aNai, which in tum will cause a decrease in the rate of Na+ pumping across the basolateral membrane. In some cases, however, there are no measurable changes in intracellular ion activity, or they are too small to account for the effect at the contralateral membrane. An example is the steady-state effect of galactose on Na+ transport in amphibian small intestine: the short-circuit current is in creased severalfold, whereas aNai does not change significantly

(21). Ex

amples in Necturus gallbladder epithelium are the effect of cAMP (fluid transport is virtually abolished while aNai is only moderately decreased,

44),

the effect of ouabain (the long-term decrease in basolateral Na+ extrusion causes a reduction in Na+ entry across the apical membrane,

22), and the

effect of HC03 - /C02 (net NaCI and fluid absorption increase without

appreciable changes in aNai or aCli,

35, 61). Although the mechanisms

linking transport rates at the cell membranes are not fully understood, it is useful to discuss two specific examples of parallel changes in apical and basolateral membrane ion transport.

Steady-State Inhibitory Effects of cAMP The dominant effects of cAMP on gallbladder epithelial cells are exerted at the apical membrane and consist of activation and/or insertion of Cl- chan nels and inhibition of both Na+/H+ and Cl-/HC03- exchangers (see above). The observation that transepithelial fluid transport is abolished with maximal intracellular cAMP levels

(30) implies that net transepithelial salt

transport must be abolished as well. Therefore, in the steady-state, net Na+


370


and CI- fluxes at each membrane are either zero or balanced by counterflux of another ion. For instance, net Na+ absorption might be balanced by K+ secretion and Cl- absorption could be balanced by HC03 - secretion. In Necturus gallbladder, the inhibition of CI-IHC03- exchange, even by maximal concentrations of cAMP, is not complete (see above), which sug gests that net apical membrane Cl- influx via anion exchange is balanced by electrodiffusive Cl- exit across the same membrane (37), or by secretion of another anion. Similarly, the maximal inhibition of apical membrane Na+ IH+ exchange by cAMP is 50%, which suggests that additional effects abolish net entry, or that cation (e. g. K +) secretion balances Na+ absorption. In either case, it is likely that net Na+ extrusion across the basolateral membrane is reduced because of the fall in aNaj and perhaps other factors. �

Steady-State Stimulatory Effects of HC03 -/C02 In gallbladders from several species, exposure to HC03 -ICOTbuffered solu tions elevates the rate of fluid absorption. This effect is caused by stimulation of NaCI absorption and in some cases to NaHC03 transport per se (for review, see 13). Exposure to HC03-IC02 stimulates NaCI entry across the apical membrane, as indicated by the increases in cell volume and cell Na+ and Cl contents (6, 7). The most likely mechanism for these effects is stimulation of both cation and anion exchangers at the apical membrane (19, 35). Apical membrane Na+/H+ exchange could be stimulated by the decrease in pHj in HC03 --buffered, compared to HEPES-buffered, solutions. The fall in pHj is small, but in the range of highest sensitivity of the cation exchanger; ex trapolations based on the measured effect of pHj on Na + entry suggest that it could account for the increase in transepithelial Na+ transport (1, 52). Cer tainly other factors could participate in the stimulation of Na+ absorption. The stimulation of apical membrane CI-IHC03 - exchange in HC03/C02 media is probably a direct consequence of the elevation of intracellular HC03 - (40), but allosteric activation of a NaCI cotransporter has also been proposed for rabbit gallbladder (7). Since both apical membrane Na+ entry and transepithelial fluid transport increase in HC03 -/C02 media, basolateral membrane Na+ extrusion must be stimulated in the absence of steady-state changes in aNai (35, 61). The mechanism of this effect is unknown. Basolateral membrane gCl- and gK+ increase in 10 mM HC03 -11% CO2, The elevation of gCI- contributes to the increase in transepithelial Cl transport and accounts almost exactly for the HC03 -ICOTdependent com ponent of net Cl- absorption (55). The parallel increases in K+ and Cl extrusion across the basolateral membrane contribute to regulate cell volume and ionic composition in the face of the increased rates of NaCl entry across the apical membrane and K+ uptake by the Na+ pump (52, 54). It is possible that the mechanisms of change in basolateral ion transport


371

rates during cAMP-induced inhibition and HC03 -ICOrinduced stimulation of transport involve changes in cell volume: cell volume decreases in response to elevation of cAMP levels and increases with elevation of mucosal solution CO2 (C. Cotton, L. Reuss, unpublished observations). The links between cell volume and basolateral ion transport rates, however, have not been es tablished.


ACKNOWLEDGMENTS

We thank Dr. C. U. Cotton for comments on a preliminary version of this review and L. Durant for secretarial help. This work was supported by National Institutes of Health grants DK-38734 and GM-OnOO. G. Altenberg is a post-doctoral fellow of Consejo Nacional de Investigaciones Cientificas y Tecnicas de la Republica Argentina.

Literature Cited 1. Altenberg, G. A., Reuss, L. 1990. Apical membrane Na+/H+ exchange in Necturus gallbladder epithelium: Its de pendence on extracellular and in tracellular pH and on external Na+ con centration. J. Gen. Physiol. 95:369-92 2. Aronson, P. S., Nee, J., Suhm, M. A. 1982. Modifier role of internal H+ in activating the Na+-H+ exchanger in re nal mirovillus membrane vesicles. Na ture 299:161-63 3. Bello-Reuss, E., Grady, T. P., Reuss, L. 1981. Mechanism of the effect of cyanide on cell membrane potential in Necturus gallbladder epithelium. J. Physiol. 314:343-57 4. Copello, J., Segal, Y., Reuss, L. 1991. Cytosolic pH regulates maxi K+ chan nels in gallbladder epithelial eells. J. Physiol. In press 5. Corcia, A., Armstrong, W. McD. 1983. KCl colransport: A mechanism for baso lateral chloride exit in Necturus gallblad der. J. Membr. Bioi. 76:173-82 6. Cremaschi, D., Henin, S . , Meyer, G. 1979. Stimulation of HC03 - of Na+ transport in rabbit gallbladder. J. Membr. BioI. 47:145-70 7. Cremaschi, D., Meyer, G., Rosetti, C. 1983. Bicarbonate effects, electromotive forces and potassium effluxes in rabbit and guinea-pig gallbladder. J. Physiol. 335:51-64 8. Cremaschi, D., Meyer, G., Rosetti, C., Botta, G., Palestini, P. 1987. The nature of the neutral Na+ -Cl- coupled entry at the apical membrane of rabbit gallblad der epithelium. I. Na+ /H+, cr tHC03double exchange and Na+ -Cl- symport. J. Membr. BioI. 95:209-18

9. Davis, C. W., Finn, A. L. 1985. Effects of mucosal sodium removal on cell volume in Necturus gallbladder epithe lium. Am. J. Physiol. 249:C304-12 10. Diamond, J. M. 1968. Transport mech anisms in the gallbladder. In Handbook of Physiology: Section 6, Alimentary Canal, Bile, Digestion, Ruminal Physiology, ed. W. Heidel, C. F. Cole, V:2451-2482. Bethesda, MD: Am. Physio!. Soc. 11. Finn, A. L., Tsai, L.-M., Falk, R. J. 1989. Monoclonal antibodies to the apical chloride channel in Necturus gall bladder inhibit the chloride conductance. Proc. Natl. Acad. Sci. USA 86:7649-52 12. Frindt, G., Palmer, L. G. 1988. Low conductance K channels in apical mem brane of rat cortical collecting tubule. Am. J. Physiol. 256:F l 43-51 13. Frizzell, R. K., Heintze, K. 1980. Transport functions of the gallbladder. In International Review of Physiology: Liver and Biliary Tract Physiology I, ed. N. B. Javitt. pp. 221-247. Baltimore: Univ. Park 14. Garcia-Diaz, J. F., Nagel, W., Essig, A. 1983. Voltage-dependent K con ductance at the apical membrane of Nec turus gallbladder. Biophys. J. 43:26978 15. Gogelein, H., Van Driessche, W. 1981. Noise analysis of the K + current through the apical membrane of N ecturus gall bladder. J. Membr. BioI. 60:187-98 16. Gogelein, H., Van Driessche, W. 1981. The effect of electrical gradients on cur rent fluctuations and impedance re corded from Necturus gallbladder. J. Membr. BioI. 60:199-209


372


17. Gunter-Smith, P. J. 1988. Apical mem brane potassium conductance in guinea pig gallbladder epithelial cells. Am. J. Physiol. 254:C808-15 18. Gunter-Smith, P. J., Schultz, G. 1982. Potassium transport and intracellular potassium activities in rabbit gallblad der. J. Membr. Bioi. 65:41-47 19. Heintze, K., Petersen, K.-U. 1980. Na/ H and CVHC03 - exchange as a mech anism for HCO, --stimulated NaCI absorption by gallbladder. In Hydrogen Ion Transport in Epithelia, ed. I. Schultz, G. Sachs, J. G. Forte, K. J. Ullrich, pp. 345-354. Amsterdam: Else vier/North Holland 20. Henin, S., Cremaschi, D. 1975. Trans cellular ion route in rabbit gallbladder. Electrical properties of the epithelial cells. Pflugers Arch. 355:125-39 21. Hudson, R. L., Schultz, S. G. 1984. Sodium-coupled sugar transport: effects on intracellular sodium activities and sodium-pump activity. Science 22 4: 1237-39 22. Jensen, P. K., Fisher, R. S., Spring, K. R. 1984. Feedback inhibition of NaCI entry in Necturus gallbladder epithelial cells. J. Membr. Bioi. 82:95-104 23. Karniski, L. P., Aronson, P. S. 1985. Chloride/formate exchange with formic acid recycling: A mechanism of active chloride transport across epithelial mem branes. Proc. Natl. Acad. Sci. USA 82:6362-65 24. Larson, M., Spring, K. R. 1983. Bume tanide inhibition of NaCl transport by Necturus gallbladder. J. Membr. Bioi. 74:123-29 25. Latorre, R., Oberhauser, A., Labarca, P., Alvarez, O. 1989. Varieties of cal cium-activated potassium channels. Annu. Rev. Physiol. 51:385-400 26. Maruyama, Y., Matsunaga, H., Hoshi, T. 1986. Ca2+ - and voltage activated K+ channel in apical cell membrane of gallbladder epithelium from Triturus. Pf/iigers Arch. 406:563-567 27. Mason, M. J., Smith, J. D., Garcia Soto, J. De J., Grinstein, S. 1989. In ternal pH-sensitive site couples cr HC03 - exchange to Na+ -H+ antiport in lymphocytes. Am. J. Physiol. 256: C428-33 28. O'Grady, S. M., Wolters, P. J., Hilde brand, K., Brown, D. R. 1989. Regula tion of ion transport in porcine gallblad der: effects of VIP and norepinephrine. Am. J. Physiol. 257:C52-57 29. Olsnes, S., Tonnessen, T. I., Ludt, J., Sandvig, K. 1987. Effect of intracellular pH on the rate of chloride uptake and

30.

31.

32.

33.

34.

35.

36.

37.

efflux in different mammalian cell lines. Biochemistry 26:2778-85 Petersen, K.-U., Reuss, L. 1983. Cyclic AMP-induced chloride permeability in the apical membrane of Necturus gall bladder epithelium. J. Gen. Physiol. 81:705-9 Petersen, K.-U., Wehner, F., Winterha ger, J. M. 1985. Na/H exchange at the apical membrane of guinea-pig gallblad der epithelium: properties and inhibition by cyclic AMP. Pf/iigers Arch. 405: S115-20 Reuss, L. 1979. Electrical properties of the cellular transepithelial pathway in Necturus gallbladder. III. Ionic per meability of the basolateral cell mem brane. J. Membr. Bioi. 47:239-59 Reuss, L. 1981. Potassium transport mechanisms by amphibian gallbladder. In Ion Transport by Epithelia, ed. S. G. Schultz. pp. 108-128. New York: Raven Reuss, L. 1983. Basolateral KCl co transport in a NaCl-absorbing epithe lium. Nature 305:723-26 Reuss, L. 1984. Independence of apical membrane Na+ and Cl- entry in Nectur us gallbladder epithelium. J. Gen. Phys iol. 84:423-45 Reuss, L. 1987. Cyclic AMP inhibits Cl-IHC03 - exchange at the apical membrane of Necturus gallbladder epithelium. J. Gen. Physiol. 90: 172-96 Reuss, L. 1989. Ion transport across gallbladder epithelium. Physiol. Rev.

69:503-45

38. Reuss, L. 1989. Regulation of trans epithelial chloride transport by amphi bian gallbladder epithelium. Ann. NY Acad. Sci. 574:370-84 39. Reuss, L. 1990. Salt and water transport by the gallbladder epithelium. In: Hand book of Physiology, The Gastrointestin al System, Intestinal Transport, 4: Beth esda, MD: Am. Physio\' Soc. In press 40. Reuss, L., Costantin, L. 1984. CI-/ HC03 - exchange at the apical mem brane of Necturus gallbladder. J. Gen. Physiol. 83:801-18 41. Reuss, L., Costantin, J. L., Bazile, J. E. Diphenylamine-2-carboxylate 1987. blocks CI- -HC03- exchange in Nectur us gallbladder epithelium. Am. J. Physi01. 253:C79-89 42. Reuss, L., Finn, A. L. 1975. Electrical properties of the cellular transepithelial pathway in Necturus gallbladder. I. Cir cuit analysis and steady-state effects of mucosal solution ionic substitution. J. Membr. Bioi. 25:115-39 43. Reuss, L., Finn, A. L. 1975. Electrical

ION TRANSPORT IN GALLBLADDER properties of the cellular transepithelial pathway in Necturus gallbladder. II. Ionic

44.


45.

46.

47.

48.

penneability of the

apical

cell

membrane. J. Membr. BioI. 25:14161 Reuss, L., Petersen, K.-U. 1985. Cyclic AMP inhibits Na+/H+ exchange at the apical membrane of Necturus gallblad der epithelium. J. Gen. Physiol. 85: 409-25 Reuss, L., Sto ddard, J. S. 1987. Rolc of H+ and HC03- in salt transport in gall bladder epithelium. Annu. Rev. Physiol. 49:35-49 Schultz, S. O. 1981. Homocellular reg ulatory mechanisms in sodium-trans porting epithelia: avoidance of extinc tion by "flush-through". Am. J. Physiol. 241:F579-90 Segal, Y., Reuss, L. 1989. Cl- channcls in cyclic AMP-stimulated gallbladder epithelium. FASEB J. 3:A862 Segal, Y., Reuss, L. 1990. Maxi K+ channels and their relationship to the

apical membrane conductance in Nectur us gallbladder epithelium. J. Gen. Phys

iol. 95:791-818 49. Segal, Y., Reuss, L. 1990. Baz+, TEA+ and quinine effects on apical membrane K+ conductance and maxi K+ channels in gallbladder epithelium. Am. J. Physi01. 259:C56-68 50. Spring, K. R., Ericson, A.-C. 1982. Epithelial cell volume modulation and regulation. J. Membr. Biol. 69:16776 51. Stewart, C. P., Winterhager, J. M., Heintze, K., Petersen. K.-U. 1989. Electrogenic bicarbonate secretion by guinea pig gallbladder epithelium apical membrane exit. Am. J. Physiol. 256: C736-49 52. Stoddard, J., Reuss, L. 1988. Depen dence of cell membrane conductances on bathing solution HC03 -ICOz in Nectur us gallbladder. J. Membr. Biol. 102: 163-74 53. Stoddard, J. S., Reuss, L. 1988. Vol tage- and time-dependence of apical membrane conductance during current

clamp in Necturus gallbladder epithe lium. J. Membr. Bioi. 103:191-204 54. Stoddard, J. S., Reu ss, L. 1989.

Electrophysiologic effects of mucosal

CI - removal in Necturus gallbladder

373

epithelium. Am. J. Physiol. 257:C56878 55. Stoddard, J. S., Reuss, L. 1989. pH effects on basolateral membrane ion conductances in gallbladder epithelium. Am. J. Physiol. 256:CI184-95 56. Tsai, L.-M., Rosenberg, R. L., Finn, A. L., Falk, R. J. 1990. Reconstitution of a chloride channel from Necturus gall bladder (NOB); blockade by specific antibody. FASEB J. 4A550 57. Van Os, C. H., Slegers, J. F. O. 1975. The electrical potential profile of gall bladder epithelium. J. Membr. Bioi. 24: 341-63 58. Wangemann, P., Wittner, M., DiStef ano, A., Englert, H. C., Lang, H. J., et at. 1986. CI- channel blockers in the thick ascending limb of the loop of Henle. Structure activity relationship Pfluger.. Arch. 407:S128-41 59. Wehner, F., Garretson, L., Dawson, K., Segal, Y., Reuss, L. 1990. A non enzymatic preparation of epithelial baso lateral membrane for patch clamp. Am. J. Physiol. 258:C1159-64 60. Weinmann, S. A., Reuss, L. 1982. Na+ -H+ exchange at the apical mem brane of Necturus gallbladder. Ex tracellular and intracellular pH studies. J. Gen. Physiol. 80:299-321 61. Weinmann, S. A., Reuss, L. 1984. Na+ -H+ exchange and Na + entry across the apical membrane of Necturus gall bladder. J. Gen. Physiol. 83:57-74 62. Winterhager, J. M., Stewart, C. P., Hcintze, K., Petersen, K.-U. 1986. Electroneutral secretion of bicarbonate by guinea pig gallbladder epithelium. Am. J. Physiol. 250:C617-28 63. Wood, J. R., Svanvik, J. 1983. Gall bladder water and electrolyte transport and its regulation. Gut 24:579-93 64. Zeldin, D. c., Corcia, A., Armstrong, W. McD. 1985. Cyclic AMP-induced .

changes in membrane conductance of

Necturus gallbladder epithelial cells. J. Membr. Bioi. 84:193-206 65. Zeuthen, T., Machen, T. 1984. HC03-1 CO2 stimulates Na+/H+ and C l -I HC03 exchange in Necturus gallblad der. In Hydrogen Ion Transport in Epithelia, ed. J. G. Forte, D. O. War nock, F. C. Rector, Jr. pp. 97-108. New York: Wiley -

Reoxygenation Effects on Ion Transport across Rat Colonic Epithelium.

Regulation of apical membrane ion transport in Necturus gallbladder.

The effect of acetzolamide on Ion transport across isolated sheep rumen epithelium.

The effect of ouabain on ion transport across isolated sheep rumen epithelium.

Intracellular sodium activity and sodium transport in necturus gallbladder epithelium.

Facilitated transport of urea across the toad gallbladder.

Nutrient transport pathways across the epithelium of the placenta.

Intracellular Ca2+ and regulation of ion transport across rabbit Clara cells.

Regulation of transport processes across the tonoplast.

Active ion transport pathways in the bovine retinal pigment epithelium.

AVT and IT regulate ion transport across the opercular epithelium of killifish (Fundulus heteroclitus) and gilthead sea bream (Sparus aurata).

Kinetics of macrotetrolide-induced ion transport across lipid bilayer membranes.

Transepithelial ion transport across duct cells of the salivary gland.

Ion transport across isolated antral mucosa of the rabbit.

Phloretin-induced changes in ion transport across lipid bilayer membranes.

Regulation of transepithelial ion transport and intracellular calcium by extracellular ATP in human normal and cystic fibrosis airway epithelium.

Shear stress-facilitated calcium ion transport across lipid bilayers.

Stanniocalcin-1 controls ion regulation functions of ion-transporting epithelium other than calcium balance.

Regulation of thyroid follicular volume by bidirectional transepithelial ion transport.

Erythrocyte ion regulation across inactive muscle during leg exercise.

Ion transport across the chick ileum: a good model for transport studies.

Bacterial adherence to human gallbladder epithelium.

Secondary active transport of water across ventricular cell membrane of choroid plexus epithelium of Necturus maculosus.

Osmoregulation in zebrafish: ion transport mechanisms and functional regulation.