Inhibition of Rho-Kinase Reduces Renal Na-H Exchanger Activity and Causes Natriuresis in Rat

Abstract

Rho-kinase regulates the actin cytoskeleton and therefore modulates transport. The role of Rho-kinase in Na-H exchanger (NHE) activity of rat proximal convoluted tubules (PCTs) was investigated using (R)-(ϩ)-trans-N-(4-pyridyl)-4-(1-aminoethyl)-cyclohexanecarboxamide (Y-27632), a specific inhibitor of Rho-kinase. In spontaneously hypertensive rats (SHR) and Wistar Kyoto (WKY) rats, apical and basolateral NHE activities were determined by measuring cell pH recovery following luminal NH 4 ϩ prepulse and basolateral sodium removal, respectively. Apical NHE activity was greater in 8 to 9 week old hypertensive SHR compared with WKY. Although Y-27632 suppressed pH i recovery in both strains, sensitivity was 50-fold higher in adult SHR. Y-27632 suppressed basolateral NHE in both strains with similar sensitivity. Apical NHE activity was not greater in 5-week-old, not yet hypertensive, SHR rats compared with WKY. In clearance studies, Na excretion was less in SHR than in WKY rats. Y-27632 increased Na excretion and fractional excretion Na in both strains but more so in SHR.22 Na uptake of the brush border membrane vesicle taken from Y-27632-treated rats decreased more than that from vehicletreated animals in both adult SHR and WKY. We conclude that apical NHE activity is increased in SHR PCT compared with controls and that inhibition of Rho-kinase reduces PCT NHE activities and causes natriuresis.

Involvement of Rho kinase pathway in the mechanism of renal vasoconstriction and cardiac hypertrophy in rats with experimental heart failure

“…It should be emphasized that ANG II has direct stimulatory effects on Na ϩ reabsorption, an action that could be independent of Rho kinase. Nishiki et al (24) reported recently that Y-27632 caused a natriuresis in normal and hypertensive rats by reducing the activity of the Na ϩ /H ϩ exchanger in the proximal nephron. They used a continuous infusion of a nonhypotensive dose of the drug, and because they carefully monitored MAP, they were able to discard experiments in which MAP decreased by Ͼ5% of the basal level.…”

Involvement of Rho GTPases and their regulators in the pathogenesis of hypertension

“…70,71 In vivo, high blood pressure in SHR is associated with a decreased renal Na C excretion and a significant increase in NHE3 activity. 72 These parameters are reversed by treatment with the Rock inhibitor Y27632. 72 …”

Small G Proteins in the Cardiovascular System: Physiological and Pathological Aspects

“…In fact, RhoA and Rho-kinase, by controlling the phosphorylation of MLC and, ultimately, the organization of the actin cytoskeleton, are important for NHE3 association with ezrin and actin, and this interaction is required for maintenance of the exchanger at the apical surface (159,474). In SHR, hypertension is associated with a marked increase in NHE3 activity and a decreased Na ϩ excretion (338). Inhibition of Rho-kinase by Y27632 reduces apical NHE3 activity and enhances Na ϩ excretion and total urine volume (338).…”

“…In SHR, hypertension is associated with a marked increase in NHE3 activity and a decreased Na ϩ excretion (338). Inhibition of Rho-kinase by Y27632 reduces apical NHE3 activity and enhances Na ϩ excretion and total urine volume (338). Because, in general, a natriuresis in patients with hypertension reduces blood pressure, it has been suggested that the natriuresis induced by Y27632 may contribute to its blood pressure lowering effect (474).…”