Muscarinic stimulation of gallbladder epithelium. II. Fluid transport, cell volume, and ion permeabilities.
Activation of muscarinic receptors in the fluid-absorptive epithelium of the Necturus gallbladder elevates cytosolic Ca2+ concentration, transiently hyperpolarizes the cell membrane voltages, and decreases the apparent fractional resistance of the apical membrane [G. A. Altenberg, M. Subramanyam, J. S. Bergmann, K. M. Johnson, and L. Reuss. Am. J. Physiol. 265 (Cell Physiol. 34): C1604-C1612, 1993]. In these studies, we show that at the peak of the hyperpolarization both apical and basolateral membrane resistances (Ra and Rb, respectively) decreased, but in 2-3 min Ra returned to control values while Rb rose to a level approximately 60% higher than control. The acetylcholine (ACh)-induced decrease in Ra is caused by activation of apical membrane maxi K+ channels secondary to elevation of cytosolic Ca2+ concentration. The increase in Rb is due to decreases in K+ and Cl- conductances. ACh had no effects on cell KCl content or water volume, although K+ conductance transiently increased. These results can be explained by the changes in basolateral membrane conductances. ACh did not alter fluid absorption. In conclusion, ACh has complex time-dependent effects on K+ and Cl- electrodiffusive permeabilities without measurable changes in cell volume or in the rate of transepithelial fluid transport.
Altenberg
G A
GA
Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston 77555.
Subramanyam
M
M
Reuss
L
L
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D001692:Biological Transport; D001834:Body Water / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D018118:Chloride Channels / Q000187:drug effects / Q000502:physiology*; D002712:Chlorides / Q000378:metabolism; D004553:Electric Conductivity / Q000187:drug effects; D004594:Electrophysiology / Q000379:methods; D004848:Epithelium / Q000187:drug effects / Q000502:physiology; D005704:Gallbladder / Q000502:physiology*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D009337:Necturus; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000502:physiology*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D018118:Chloride Channels; D002712:Chlorides; D015221:Potassium Channels; D011976:Receptors, Muscarinic; D013757:Tetraethylammonium Compounds; D019789:Tetraethylammonium; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium