CROMAKALIM AND PINACIDIL DILATE SMALL MESENTERIC-ARTERIES BUT NOT SMALL CEREBRAL-ARTERIES

Small elevations in external K+ hyperpolarize and dilate small cerebral arteries. The hyperpolarization and dilation to K+ are blocked by barium (< 0.1 mM). Since membrane hyperpolarization appears to be an important mechanism for dilation of these small cerebral arteries, we investigated the effects of the hyperpolarizing vasodilators, cromakalim and pinacidil, on isolated pressurized rat cerebral arteries (diameter of 158 +/- 5-mu-m at 50% of the systolic blood pressure). Cromakalin and pinacidil, which are potent relaxants of a variety of muscle types, were without effect on posterior cerebral arteries at concentrations that completely dilate similarly sized rat mesenteric arteries (diameter 134 +/- 6-mu-m at 50% of the systolic blood pressure). The mesenteric artery dilation to cromakalim and pinacidil was reversed by glibenclamide. However, unlike the cerebral arteries, mesenteric arteries did not exhibit a barium-sensitive dilation to external K+. Thus it appears that there may be differences in the types of K+ channels that are activated by dilating mechanisms in small cerebral and mesenteric arteries.