Regulation and possible physiological role of the Ca(2+)-dependent K+ channel of cortical collecting ducts of the rat.
In the luminal membrane of rat cortical collecting duct (CCD) a big Ca(2+)-dependent and a small Ca(2+)-independent K+ channel have been described. Whereas the latter most likely is responsible for the K+ secretion in this nephron segment, the function of the large-conductance K+ channel is unknown. The regulation of this channel and its possible physiological role were examined with the conventional cell-free and the cell-attached nystatin patch-clamp techniques. Patch-clamp recordings were obtained from the luminal membrane of isolated perfused CCD segments and from freshly isolated CCD cells. Intracellular calcium was measured using the calcium-sensitive dye fura-2. The large-conductance K+ channel was strongly voltage- and calcium-dependent. At 3 mumol/l cytosolic Ca2+ activity it was half-maximally activated. At 1 mmol/l it was neither regulated by cytosolic pH nor by ATP. At 1 mumol/l Ca2+ activity the open probability (Po) of this channel was pH-dependent. At pH 7.0 Po was decreased to 4 +/- 2% (n = 9) and at pH 8.5 it was increased to 425 +/- 52% (n = 9) of the control. At this low Ca2+ activity the Po of the channel was reduced by 1 mmol/l ATP to 8 +/- 4% (n = 6). Cell swelling activated the large-conductance K+ channel (n = 14) and hyperpolarized the membrane potential of the cells by 9 +/- 1 mV (n = 23). Intracellular Ca2+ activity increased after hypotonic stress. This increase depended on the extracellular Ca2+ activity.(ABSTRACT TRUNCATED AT 250 WORDS)
Hirsch
J
J
Albert-Ludwigs-Universität, Physiologisches Institut, Freiburg, Federal Republic of Germany.
Leipziger
J
J
Fröbe
U
U
Schlatter
E
E
D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000502:physiology*; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004594:Electrophysiology; D005260:Female; D016257:Fura-2; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007672:Kidney Cortex / Q000187:drug effects / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000187:drug effects / Q000378:metabolism*; D008564:Membrane Potentials / Q000502:physiology; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D009761:Nystatin / Q000494:pharmacology; D010477:Perfusion; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D015221:Potassium Channels; D009761:Nystatin; D000255:Adenosine Triphosphate; D002118:Calcium; D016257:Fura-2