Subarachnoid hemorrhage and the role of potassium channels in relaxations of canine basilar artery to nitrovasodilators

This study was designed to determine the effect of subarachnoid hemorrhage (SAH) on potassium (K⁺) channels involved in relaxations of cerebral arteries to nitrovasodilators. The effects of K⁺ channel inhibitors on relaxations to 3-morpholinosydnonimine (SIN-1) and sodium nitroprusside (SNP) were studied in rings of basilar arteries obtained from untreated dogs and dogs exposed to SAH. The levels of cyclic GMP were measured by radioimmunoassay. In rings without endothelium, concentration-dependent relaxations to SIN-1 (10^-9 - 10^-4 mol/L) and SNP (10^-9 - 10^-4 mol/L) were not affected by SAH, whereas increase in cyclic GMP production stimulated by SIN-1 (10^-6 mol/L) was significantly suppressed after SAH. The relaxations to SIN- 1 and SNP were reduced by charybdotoxin (CTX; 10^-7 mol/L), a selective Ca²⁺-activated K⁺ channel inhibitor, in both normal and SAH arteries; however, the reduction of relaxations by CTX was significantly greater in SAH arteries. By contrast, the relaxations to these nitrovasodilators were not affected by glyburide (10^-5 mol/L), an ATP- sensitive K⁺ channel inhibitor, in both normal and SAH arteries. These findings suggest that in cerebral arteries exposed to SAH, Ca²⁺-activated K⁺ channels may play a compensatory role in mediation of relaxations to nitric oxide. This may help to explain mechanisms of relaxations to nitrovasodilators in arteries with impaired production of cyclic GMP.