Coronary arteriolar flow-induced vasodilation signals through tyrosine kinase.

Abstract

Coronary arterioles demonstrate flow-dependent vasodilation that is mediated by endothelial release of nitric oxide. The signaling mechanisms for this response remain unknown. Because tyrosine kinases are an enzyme family linked to many signaling pathways, including some for mechanosensitive transduction, we hypothesized that tyrosine kinase activation is a critical step in flow-induced vasodilation. To test this hypothesis, coronary arterioles were isolated, cannulated with micropipettes, and perfused by two independent reservoir systems. Intraluminal pressure was set at 60 cmH2O, and flow was generated by changing the heights of the reservoirs in equal and opposite directions, thus establishing a pressure difference across the arteriole without altering intraluminal pressure. Vasodilatory responses to intraluminal flow and substance P (1 x 10(-12) to 1 x 10(-7) M) were evaluated before and after intraluminal application of the tyrosine kinase inhibitors genistein (5 microM) and piceatannol (10 microM). Exposure to these inhibitors did not alter spontaneous tone. Substance P caused dose-dependent vasodilation that was not affected by genistein or piceatannol. Increases in intraluminal flow (generated by pressure differences ranging from 4 to 60 cmH2O) elicited graded increases in diameter. Both genistein and piceatannol inhibited the vasodilatory responses to flow. Treatment with daidzein, an inactive analogue of genistein, had no effect on either the flow-induced responses or substance P-induced vasodilation. To further confirm that tyrosine kinase activation is involved in flow-induced vasodilation, vessels were exposed to flow in the absence or presence of genistein and subsequently stained with a fluorescein isothiocyanate-labeled phosphotyrosine antibody. Exposure to flow significantly increased fluorescence of endothelial cells. Genistein treatment reversed the flow-induced increase in tyrosine phosphorylation. These results indicate that endothelium-dependent, flow-induced vasodilation in isolated porcine coronary arterioles is accompanied by an increase in tyrosine kinase activity. We conclude that endothelium-dependent, nitroxidergic, flow-induced vasodilation is mediated, at least in part, by a signaling pathway involving a tyrosine kinase.