Are voltage-dependent ion channels involved in the endothelial cell control of vasomotor tone?

In the microcirculation, longitudinal conduction of vasomotor responses provides an essential means of coordinating flow distribution among vessels in a complex network. Spread of current along the vessel axis can display a regenerative component, which leads to propagation of vasomotor signals over many millimeters; the ionic basis for the regenerative response is unknown. We examined the responses to 10 s of focal electrical stimulation (30 Hz, 2 ms, 30 V) of mouse cremaster arterioles to test the hypothesis that voltage-dependent Na+ (Na-v) and Ca2+ channels might be activated in long-distance signaling in microvessels. Electrical stimulation evoked a vasoconstriction at the site of stimulation and a spreading, nondecremental conducted dilation. Endothelial damage (air bubble) blocked conduction of the vasodilation, indicating an involvement of the endothelium. The Nav channel blocker bupivacaine also blocked conduction, and TTX attenuated it. The Nav channel activator veratridine induced an endothelium-dependent dilation. The Nav channel isoforms Na(v)1.2, Na(v)1.6, and Na(v)1.9 were detected in the endothelial cells of cremaster arterioles by immunocytochemistry. These findings are consistent with the involvement of Nav channels in the conducted response. BAPTA buffering of endothelial cell Ca2+ delayed and reduced the conducted dilation, which was almost eliminated by Ni2+, amiloride, or deletion of alpha(1H) T-type Ca2+ (Ca(v)3.2) channels. Blockade of endothelial nitric oxide synthase or Ca2+-activated K+ channels also inhibited the conducted vasodilation. Our findings indicate that an electrically induced signal can propagate along the vessel axis via the endothelium and can induce sequential activation of Nav and Cav3.2 channels. The resultant Ca2+ influx activates endothelial nitric oxide synthase and Ca2+-activated K+ channels, triggering vasodilation.