Cyclic AMP-induced changes in membrane conductance of Necturus gallbladder epithelial cells.
Enhanced cellular cAMP levels have been shown to increase apical membrane Cl- and HCO3- conductances in epithelia. We found that the phosphodiesterase inhibitor 3-isobutyl-1-methyl-xanthine (IBMX) increases cAMP levels in Necturus gallbladder. We used conventional open-tip and double-barreled Cl- -selective microelectrodes to study the effects of IBMX on membrane conductances and intracellular Cl- activities in gallbladders mounted in a divided chamber and bathed with Ringer's solutions at 23 degrees C and pH 7.4. In HCO3- -free media, 0.1 mM IBMX added to the mucosal medium depolarized the apical membrane potential Va, decreased the fractional resistance FR, and significantly reduced intracellular Cl- activity (aCli). Under control conditions, aCli was above the value corresponding to passive distribution across the apical cell membrane. In media containing 25 mM HCO3-, IBMX caused a small transient hyperpolarization of Va followed by a depolarization not significantly different from that observed in HCO3- -free Ringer's. Removal of mucosal Cl-, Na+ or Ca2+ did not affect the IBMX-induced depolarization in Va. The basolateral membrane of Necturus gallbladder is highly K+ permeable. Increasing serosal K+ from 2.5 to 80 mM, depolarized Va. Mucosal IBMX significantly reduced this depolarization. Addition of 10 mM Ba2+, a K+ channel blocker, to the serosal medium depolarized Va and, essentially, blocked the depolarization induced by IBMX. These results indicate that mucosal IBMX increases apical HCO3- conductance and decreases basolateral K+ conductance in gallbladder epithelial cells via a cAMP-dependent mechanism. The latter effect, not previously reported in epithelial tissues, appears to be the major determinant of the IBMX-induced depolarization of Va.
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D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology*; D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism*; D004553:Electric Conductivity / Q000187:drug effects; D004848:Epithelium / Q000187:drug effects / Q000502:physiology; D005704:Gallbladder / Q000502:physiology*; D066298:In Vitro Techniques; D007700:Kinetics; D008433:Mathematics; D008564:Membrane Potentials / Q000187:drug effects; D008954:Models, Biological; D009092:Mucous Membrane / Q000502:physiology; D009337:Necturus; D013806:Theophylline / Q000031:analogs & derivatives*
D001639:Bicarbonates; D002712:Chlorides; D013806:Theophylline; D000242:Cyclic AMP; D015056:1-Methyl-3-isobutylxanthine