The α₂-isoform of Na-K-ATPase mediates ouabain-induced hypertension in mice and increased vascular contractility in vitro

Abstract

. The ␣ 2-isoform of Na-K-ATPase mediates ouabain-induced hypertension in mice and increased vascular contractility in vitro. Am J Physiol Heart Circ Physiol 288: H477-H485, 2005. First published September 30, 2004 doi:10.1152/ajpheart.00083.2004.-Although ouabain is known to induce hypertension, the mechanism of how this cardiac glycoside affects blood pressure is uncertain. The present study demonstrates that the ␣2-isoform of the Na-K-ATPase mediates the pressor effects of ouabain in mice. To accomplish this, we analyzed the effect of ouabain on blood pressure in wild-type mice, where the ␣2-isoform is sensitive to ouabain, and genetically engineered mice expressing a ouabain-insensitive ␣2-isoform of the Na-K-ATPase. Thus differences in the response to ouabain between these two genotypes can only be attributed to the ␣2-isoform of Na-K-ATPase. As the ␣1-isoform is naturally resistant to ouabain in rodents, it will not be inhibited by ouabain in either genotype. Whereas prolonged administration of ouabain increased levels of ouabain in serum from both wild-type and targeted animals, hypertension developed only in wild-type mice. In addition, bolus intravenous infusion of ouabain increased the systolic, mean arterial, and left ventricular blood pressure in only wild-type anesthetized mice. In vitro, ouabain increased vascular tone and thereby phenylephrine-induced contraction of the aorta in intact and endothelium-denuded wild-type mice but in ␣2-resistant mice. Ouabain also increased the magnitude of the spontaneous contractions of portal vein and the basal tone of the intact aorta from only wild-type mice. The increase in aortic basal tone was dependent on the presence of endothelium. Our studies also demonstrate that the ␣ 2-isoform of Na-K-ATPase mediates the ouabain-induced increase in vascular contractility. This could play a role in the development and maintenance of ouabain-induced hypertension.

How does salt retention raise blood pressure?

“…Elevated EO levels were also observed in rodents with DOCA-salt hypertension (41,43), ACTH-hypertension (20, 20a, 115), reduced renal mass hypertension (108), and in salt-sensitive Milan strain rats on a high-salt diet (22,23). Indeed, a critical corollary to these reports is the evidence that prolonged administration of ouabain, itself (a Strophanthus steroid), but not digoxin or digitoxin (Digitalis steroids), elevates BP in normal rats and mice (19,60,72,74,75,116).…”

“…In related studies, Lingrel and colleagues have shown that transgenic mice with a mutated ␣ 2 Na ϩ pump that renders this isoform resistant to ouabain are resistant to both ouabaininduced hypertension (19) and ACTH-induced hypertension (20, 20a). Moreover, the plasma from mice with ACTHinduced hypertension had significantly elevated levels of a water-soluble substance that cross-reacted with antidigoxinspecific Fab fragments (Digibind) (20).…”

Subunit Composition and Role of Na+,K+-ATPases in Ventricular Myocytes

“…The α3 subunit was originally indicated to be present in the membrane in the vicinity of Ca 2+ store sites in blood smooth muscle cells [6,26] but a recent knockout experiment suggests the presence of the α2 in such a membrane domain of smooth muscle cells [27]. As a result, the α2 subunit localized in the plasma membrane closely associated with Ca 2+ store sites may be α2 irrespective of the cell type.…”

The highly conserved cardiac glycoside binding site of Na,K-ATPase plays a role in blood pressure regulation

“…Tail-cuff measurements were obtained by using a Visitech (Apex, NC) system computerized apparatus, as described in ref. 32. In brief, for each measurement, 10 preliminary blood pressure measurements were obtained to acclimate the mice to the apparatus, and these were followed by 10 recorded SBP and heart rate measurements.…”