Pinacidil opens K+‐selective channels causing hyperpolarization and relaxation of noradrenaline contractions in rat mesenteric resistance vessels

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Abstract
1 The effects of pinacidil on noradrenaline-induced tone, smooth muscle membrane potential and42 K- and86 Rb-efllux from isolated mesenteric resistance vessels (internal diameter 200 μm) of the rat have been studied. 2 Pinacidil (0.3–10 μM) produced concentration-dependent suppression of noradrenaline-induced tone. 3 Pinacidil (0.3–10 μM) caused concentration-dependent hyperpolarization of the smooth muscle. 4 In rat resistance vessels loaded with42 K, pinacidil (1–10 μM) significantly increased the42 K-efllux rate constant. 5 With the use of86 Rb as a marker for K+, 1 μM pinacidil did not affect the86 Rb-efflux rate constant, while 10 μM pinacidil transiently increased the86 Rb rate constant. 6 The results indicate that the relaxant action of pinacidil in these vessels is due to the opening of K+-channels and consequent hyperpolarization. The K+-channels opened are selective for42 K over86 Rb.