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

Contraction of vascular smooth muscle is regulated primarily by calcium concentration and secondarily by ROCK activity within the cells. In contrast to the wealth of information regarding regulation of calcium concentration, little is known about the spatiotemporal regulation of ROCK activity in live blood vessels. Here, we report ROCK activation in subcutaneous arterioles in a transgenic mouse line that expresses a genetically encoded ROCK biosensor based on the principle of F0rster resonance energy transfer by two-photon excitation in vivo imaging. Rapid vasospasm was induced upon laser ablation of arterioles, 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 after irradiation. 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 and then maintained by sympathetic nerve-mediated ROCK activation.

Automated summary

The contraction of vascular smooth muscle is primarily regulated by calcium concentration and secondarily regulated by ROCK activity. In this study, ROCK activation was observed in subcutaneous arterioles using a genetically encoded biosensor. Vasospasm was induced by laser ablation, accompanied by a transient increase in calcium concentration, and ROCK activation continued for several minutes post-irradiation. The findings suggest that vasoconstriction is initially triggered by a rapid surge of cytoplasmic calcium and then maintained by sympathetic nerve-mediated ROCK activation.