Potassium channels in epithelial cells.
The broad array of K- channels in epithelial cells includes voltage-dependent (mainly outward) and Ca(2+)-activated channels, and K+ channels modulated by adenosine triphosphate (ATP). Voltage-dependent K+ channels mediate Na+/K+ absorption and secretion; typically, they are found in the basolateral membrane and exhibit burst activity. Ca(2+)-activated K+ (Ca2+/K+) channels regulate activity by decreasing Ca2+ influx via voltage-gated Ca2+ channels. Ca2+/K+ channels exhibit conductances of 4-300 pS, and have a low open probability (< 10(-7)) at the level of the resting membrane potential. ATP-sensitive channels have been observed mainly in insulin-secreting pancreatic beta-cells and in the urinary tract, where the open state is rapidly closed by ATP. The channels are voltage-dependent, exhibit burst activity, and, in the case of the urinary-tract cells, are Ca2+ dependent. Chemical compounds that selectively open or block K+ channels have been exploited to characterize channels found in different cells, but no opener or blocker has been found that specifically affects only one type of K+ channel. Specialized model systems and recombinant techniques have led to a general understanding of the structure of K+ channels, but many important details remain to be determined.
Department of Orthopaedic Surgery, Louisiana State University Medical Center, Shreveport 71130-3932.
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D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000494:pharmacology / Q000502:physiology; D004848:Epithelium / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000502:physiology; D015640:Ion Channel Gating / Q000187:drug effects; D008564:Membrane Potentials; D051379:Mice; D008954:Models, Biological; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000145:classification / Q000187:drug effects / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology
D015221:Potassium Channels; D000255:Adenosine Triphosphate; D019204:GTP-Binding Proteins; D011188:Potassium; D002118:Calcium