Abstract
Inhibition of the Na,K-ATPase by ouabain potentiates vascular tone and agonist-induced contraction. These effects of ouabain varies between different reports. In this study, we assessed whether the pro-contractile effect of ouabain changes with arterial diameter and the molecular mechanism behind it. Rat mesenteric small arteries of different diameters (150–350 µm) were studied for noradrenaline-induced changes of isometric force and intracellular Ca2+ in smooth muscle cells. These functional changes were correlated to total Src kinase and Src phosphorylation assessed immunohistochemically. High-affinity ouabain-binding sites were semi-quantified with fluorescent ouabain. We found that potentiation of noradrenaline-sensitivity by ouabain correlates positively with an increase in arterial diameter. This was not due to differences in intracellular Ca2+ responses but due to sensitization of smooth muscle cell contractile machinery to Ca2+. This was associated with ouabain-induced Src activation, which increases with increasing arterial diameter. Total Src expression was similar in arteries of different diameters but the density of high-affinity ouabain binding sites increased with increasing arterial diameters. We suggested that ouabain binding induces more Src kinase activity in mesenteric small arteries with larger diameter leading to enhanced sensitization of the contractile machinery to Ca2+.
Highlights
IntroductionA prolonged inhibition of the Na,K-ATPase by cardiac glycosides, for example, ouabain, leads to chronic elevation of blood pressure in rodents [2,3,4,5,6]
The Na,K-ATPase is strongly suggested to be implicated in hypertension [1]
To understand the molecular mechanism responsible for this, we assessed [Ca2+]i and Src kinase phosphorylation in these arteries when exposed to ouabain. From these experiments we conclude that the diameter-dependent effect of ouabain was not due to differences in [Ca2+]i responses in the vascular smooth muscle cells but due to sensitization of their contractile machinery to [Ca2+]i
Summary
A prolonged inhibition of the Na,K-ATPase by cardiac glycosides, for example, ouabain, leads to chronic elevation of blood pressure in rodents [2,3,4,5,6]. This can be prevented by the ouabain antagonist rostafuroxin or by an ouabain-binding antibody [7,8]. Hemodynamic changes induced by ouabain are in line with the conventional view on hypertension pathology, where elevated blood pressure is mediated by an increase in peripheral vascular resistance [11,12]
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