The effect of alkaline pH and transmural pressure on arterial constriction and membrane potential of hypertensive cerebral arteries.

These studies were undertaken to examine the effect of alkalosis to modify "pressure-induced" activation of isolated cerebral arteries from spontaneously hypertensive rats (SHR) and their normotensive Wistar-Kyoto (WKY) controls. At pH 7.4 and PCO2 of 34 torr elevation of transmural pressure from 0-140 mm Hg resulted in myogenic activation preceded by membrane depolarization in both SHR and WKY. The degree of developed myogenic tone in SHR was elevated above WKY. Alkalosis (pH 7.4-7.7) depolarized and activated SHR cerebral arteries to a greater extent than WKY. Furthermore, both the electrical and mechanical responses to elevation in transmural pressure were exaggerated in SHR compared to WKY at pH 7.7 (PCO2 constant at 34 torr). Manipulation of PCO2 at constant pH of 7.4 had similar effects on "pressure-induced" myogenic tone in both SHR and WKY. Thus, cerebral arteries from both SHR and WKY depolarize and develop myogenic tone in response to increasing transmural pressure. This response is augmented in SHR, but to a much greater extent upon elevation of extracellular pH, while PCO2 is maintained within normal limits. The implications of these findings are discussed.