Mechanism of activation of K+ channels by minoxidil-sulfate in Madin-Darby canine kidney cells.
We studied the mechanism of K+ channel activation by minoxidil-sulfate (MxSO4) in fused Madin-Darby canine kidney (MDCK) cells. Patch-clamp techniques were used to assess single channel activity, and fluorescent dye techniques to monitor cell calcium. A Ca(2+)-dependent inward-rectifying K+ channel with slope conductances of 53 +/- 3 (negative potential range) and 20 +/- 3 pS (positive potential range) was identified. Channel activity is minimal in cell-attached patches. MxSO4 initiated both transient channel activation and an increase of intracellular Ca2+ (from 94.2 +/- 9.1 to 475 +/- 12.6 nmol/liter). The observation that K+ channel activity of excised inside-out patches was detected only at Ca2+ concentrations in excess of 10 mumol/liter suggests the involvement of additional mechanisms during channel activation by MxSO4. Transient K+ channel activity was also induced in cell-attached patches by 10 mumol/liter of the protein kinase C activator 1-oleoyl-2-acetyl-glycerol (OAG). OAG (10 mumol/liter in the presence of 1.6 mmol/liter ATP) increased the Ca2+ sensitivity of the K+ channel in inside-out patches significantly by lowering the Km for Ca2+ from 100 mumol/liter to 100 nmol/liter. The channel activation by OAG was reversed by the protein kinase inhibitor H8. Staurosporine, a PKC inhibitor, blocked the effect of MxSO4 on K+ channel activation. We conclude that MxSO4-induced K+ channel activity is mediated by the synergistic effects of an increase in intracellular Ca2+ and a PKC-mediated enhancement of the K+ channel's sensitivity to Ca2+.
Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510.
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A
Schwab
J
J
Geibel
W
W
Wang
H
H
Oberleithner
G
G
Giebisch
D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000032:analysis / Q000494:pharmacology / Q000502:physiology; D002462:Cell Membrane / Q000502:physiology / Q000648:ultrastructure; D002478:Cells, Cultured; D004075:Diglycerides / Q000494:pharmacology; D004285:Dogs; D005453:Fluorescence; D007668:Kidney / Q000166:cytology* / Q000502:physiology / Q000648:ultrastructure; D008564:Membrane Potentials / Q000502:physiology; D008914:Minoxidil / Q000031:analogs & derivatives* / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology; D019311:Staurosporine
D000470:Alkaloids; D004075:Diglycerides; D015221:Potassium Channels; C039516:minoxidil sulfate ester; D008914:Minoxidil; C038237:1-oleoyl-2-acetylglycerol; D011493:Protein Kinase C; D019311:Staurosporine; D002118:Calcium