title: Ca2+- and voltage activated K+ channel in apical cell membrane of gallbladder epithelium from Triturus.
abstract: The presence of Ca2+- and voltage-activated K+ channels was directly demonstrated in the apical cell membrane of gallbladder epithelium by patch-clamp single-channel current recording. In K+-depolarized epithelial cells, negative pipette potentials induced outward current steps when the patch-pipette was filled with Na+-rich solution and these current steps were not affected by the presence or absence of Cl-. When K+-rich solution was in the pipette and K+-depolarized cells were examined, the current-voltage relations were linear with a single-channel conductance of 140 pS and polarity was reversed at 0 mV. In excised inside-out membrane patches, raising the free Ca2+ concentration of the medium facing the inner side of the membrane from 10(-7) to 10(-6) M evoked a marked increase in open state probability of the channels without affecting the elementary current steps. This suggests that intracellular Ca2+ as a second messenger plays a crucial role in the regulatory mechanism of the membrane potential by modulating the high-conductance apical K+ channels.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002462:Cell Membrane / Q000378:metabolism; D004558:Electric Stimulation; D004848:Epithelium / Q000378:metabolism; D005704:Gallbladder / Q000378:metabolism*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000502:physiology*; D008564:Membrane Potentials; D011188:Potassium / Q000378:metabolism*; D014319:Triturus
chemical_list: D007473:Ion Channels; D011188:Potassium; D002118:Calcium