Two different types of channels are targets for potassium channel openers in Xenopus oocytes

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Abstract
K+ channel openers elicit K+ currents in follicle‐enclosed Xenopus oocytes. The most potent activators are the pinacidil derivatives P1075 and P1060. The rank order of potency to activate K + currents in follicle‐enclosed oocytes was: P1075 (K0.5: 5 μM)>P1060 (K0.5: 12 μM)> BRL38227 (lemakalim) (K0.5:77 μM)>RP61419 (K0.5:100 μM)>(−)pinacidil (K0.5:300 μM). Minoxidil sulfate, nicorandil. RP49356 and diazoxide were ineffective. Activation by the K+ channel openers could be abolished by the antidiabetic sulfonylurea glibenclamide. It was not affected by the blocker of the Ca2+‐activated K+ channels charybdotoxin. The various K+ channel openers failed to activate glibenclamide‐sensitive K+ channels in defolliculated oocytes, but BRL derivatives (K0.5 for BRL38226 is 150 μM) and RP61419 inhibited a background current. The channel responsible for this background current is K+ permeable but not fully selective for K+. It is resistant to glibenclamide. It is inhibited by Ba2+, 4‐aminopyridine. Co2+,.Ni2+ and La3+.