The role of the RhoA/Rho-kinase signaling pathway in renal vascular reactivity in endothelial nitric oxide synthase null mice

Abstract

Smooth muscle contraction is regulated by the small GTPase RhoA and its target, Rho-kinase and recent evidence indicates that nitric oxide (NO) causes vasodilation through inhibition of the RhoA/Rho-kinase (ROCK) signaling pathway. This study tested the hypothesis that the enhanced renal vascular tone and systemic hypertension in endothelial nitric oxide synthase (eNOS) null mice is due to disinhibition of the ROCK signaling pathway. Systolic blood pressure (SBP) was measured by tail-cuff plethysmography and the isolated Krebs-perfused kidney preparation was used to evaluate renal vascular responses in C57BL/6 (wild type, WT) and eNOS knockout (KO) mice treated with Y-27632, a ROCK inhibitor. Compared with the WT mice, Rho kinase activity was higher in eNOS KO mice (37 +/- 8%, P < 0.05) as was SBP (33 +/- 4%, P < 0.05), basal renal perfusion pressure (31 +/- 4%, P < 0.05) and renal vascular resistance (35 +/- 4%, P < 0.05). Y-27632 abolished these differences. Vasoconstriction elicited by angiotensin II (Ang II) or phenylephrine (PE), G-protein-coupled receptor (GPCR) agonists, but not that elicited by arachidonic acid or KCl, was greater in eNOS KO mice. Y-27632 eliminated the amplified vasoconstriction elicited by Ang II or phenylephrine but to a greater extent in eNOS KO mice. Similarly, responses elicited by guanosine 5'-gamma-thiotriphosphate (GTPgammaS), a non-hydrolyzable GTP analog, or sodium tetrafluoride (NaF4), an activator of G-proteins, was greater in eNOS KO mice, 53 +/- 14 and 50 +/- 3%, respectively. Y-27632 normalized the difference. Y-27632 also elicited a dose-dependent renal vasodilation that was greater in eNOS KO mice. These results show that the ROCK signaling pathway is amplified in the eNOS KO mouse kidney and that the enhanced renal vascular tone and selective increase in reactivity to GPCR agonists supports a role for ROCK in the hypertension and vascular dysfunction in the eNOS KO mice.