Role of Rho -kinase -dependent constrictor activity in vascular smooth muscle.

Vascular tone is modulated by hormonal, neural and paracrine input for the proper regulation of blood pressure and organ perfusion. Elucidating and understanding the signaling pathway(s) involved in vascular smooth muscle contraction may aid in the prevention or successful treatment of many vascular-related end organ pathologies. Contraction of the smooth muscle cell occurs primarily via the Ca2+-dependent stimulation of myosin light chain (MLC) kinase, to lead to the phosphorylation of MLC and subsequent actin/myosin interaction. The phosphorylation of MLC is also regulated by the activity of MLC phosphatase, a process termed Ca2+-sensitization. MLC phosphatase activity is, in part, regulated by the small G-protein, RhoA, and a downstream target, Rho-kinase. The serine/threonine kinase, Rho-kinase, phosphorylates the myosin binding subunit of MLC phosphatase to inhibit phosphatase activity and thus promote the phosphorylated state of MLC. The goal of this dissertation was to determine the physiologic role and regulation of RhoA/Rho-kinase activity in vascular smooth muscle, following the general hypothesis that increased Rho-kinase activity promotes the maintenance of vasoconstriction and the inhibition of Rho-kinase signaling mediates vasodilation. Western blot analysis demonstrated RhoA and Rho-kinase protein expression in isolated rat cavernosal tissue. Using an in vivo rat model of erection, the intracavernosal injection of Y-27632, a selective Rho-kinase inhibitor, was found to result in a significant increase in intracavernosal pressure/mean arterial pressure. In vitro measurements of isometric force generation demonstrated Y-27632 to relax agonist-induced contraction of isolated rat cavernosal tissue and aorta. Additional measurements of isometric force generation of rat aorta found the inhibitory effects of Y-27632 to be attenuated in the absence of nitric oxide production or signaling, consistent with the hypothesis that Rho-kinase activity is elevated in the absence of nitric oxide. Data presented in this dissertation demonstrate a role for Rho-kinase activity in the maintenance of vascular smooth muscle contraction and provide evidence to support that the inhibition of Rho-kinase activity is a physiologic mechanism of nitric oxide-induced vasodilation.Ph.D.Animal PhysiologyBiological SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/131555/2/3057921.pd