Potassium channels modulate cerebral autoregulation during acute hypertension

We tested the hypothesis that constriction of cerebral arterioles during ac ute increases in blood pressure is attenuated by activation of potassium (K +) channels. We tested the effects of inhibitors of calcium-dependent K+ ch annels [iberiotoxin (50 nM) and tetraethylammonium (TEA, 1 mM)] on changes in arteriolar diameter during acute hypertension. Diameter of cerebral arte rioles (baseline diameter = 46 +/- 2 mu m, mean +/- SE) was measured using a cranial window in anesthetized rats. Arterial pressure was increased from a control value of 96 +/- 1 mmHg to 130, 150, 170, and 200 mmHg by intrave nous infusion of phenylephrine. Increases in arterial pressure from baselin e to 130 and 150 mmHg decreased the diameter of cerebral arterioles by 5-10 %. Greater increases in arterial pressure produced large increases in arter iolar diameter (i.e., "breakthrough of autoregulation''). Iberiotoxin or TE A inhibited increases in arteriolar diameter when arterial pressure was inc reased to 170 and 200 mmHg. The change in arteriolar diameter at 200 mmHg w as 20 +/- 3% and -1 +/- 4% in the absence and presence of iberiotoxin, resp ectively. These findings suggest that calcium-dependent K+ channels attenua te cerebral microvascular constriction during acute increases in arterial p ressure, and that increases in arteriolar diameter at high levels of arteri al pressure are not simply a passive phenomenon.