Large Ca(2+)-activated K+ channels responsive to angiotensin II in cultured human mesangial cells.
The patch-clamp method was used to determine the properties and response to angiotensin II (ANG II) of K+ channels in subpassages of human mesangial cell cultures. In cell-attached patches, with 140 mM KCl in the bath and cell potential equal to 40 mV, the open probability (Po) of large K+ channels (MKCa) was 0.8 with 0.5 mM Ca2+ in the bath and < 0.05 if the bath Ca2+ concentration was reduced to 1.0 microM. Open and closed dwell-time histograms of MKCa displayed both fast and slow time constants. Addition of ANG II (100 nM) to the bath solution (Ca2+ = 1.0 microM) increased the Po of MKCa in cyclic bursts by decreasing the time constant of the slow closed state. In excised inside-out patches, the mean single-channel conductance of MKCa was 206 pS in symmetrical 140 mM KCl. The selectivity sequence, established in asymmetrical cationic solutions, was K+ (1.0) > Rb+ (0.54) > NH+4 (0.11) > > Cs+ = Na+ (< 0.05). The Po of MKCa was increased by depolarizing potentials and high bath Ca2+. The Boltzmann distribution was consistent with an effective valence of 1.0, and the Hill coefficient for Ca2+ activation was 0.52. We conclude that MKCa has properties similar to large Ca(2+)-activated K+ channels and may act to repolarize the membrane of mesangial cells in response to an agonist-induced mobilization of intracellular Ca2+.
Stockand
J D
JD
Department of Medicine, University of Texas Health Science Center at Houston 77225.
Sansom
S C
SC
D000804:Angiotensin II / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology*; D002478:Cells, Cultured; D004594:Electrophysiology; D005920:Glomerular Mesangium / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D015221:Potassium Channels / Q000187:drug effects* / Q000378:metabolism* / Q000502:physiology; D015398:Signal Transduction
D015221:Potassium Channels; D000804:Angiotensin II; D002118:Calcium