Visualization of Spatially Controlled Vasospasm by Sympathetic Nerve-Mediated ROCK Activation.

Abstract Contraction of vascular smooth muscle is regulated primarily by calcium concentration and secondarily by ROCK activity within the cells. In contrast to the regulation of calcium concentration, little is known about the spatio-temporal regulation of ROCK activity in live blood vessels. Here, we report ROCK activation in subcutaneous arterioles in a transgenic mouse line, which expresses a genetically-encoded ROCK biosensor based on the principle of Fӧrster resonance energy transfer by two-photon excitation in vivo imaging. Upon laser ablation of arterioles, rapid vasospasm was induced, concomitant with a transient increase in calcium concentration in arteriolar smooth muscles. Unlike the increase in calcium concentration, vasoconstriction and ROCK activation continued for several minutes. Both the ROCK inhibitor, fasudil, and the ganglionic nicotinic acetylcholine receptor blocker, hexamethonium, inhibited laser-induced ROCK activation and reduced the duration of vasospasm at the segments distant from the irradiated point. These observations suggest that vasoconstriction is initially triggered by a rapid surge of cytoplasmic calcium concentration and then maintained by sympathetic nerve-mediated ROCK activation.