Na+pump α2-isoform specifically couples to contractility in vascular smooth muscle: evidence from gene-targeted neonatal mice

Abstract

The relative expression of α1- and α2-Na+/K+-ATPase isoforms found in vascular smooth muscle is developmentally regulated and under hormonal and neurogenic control. The physiological roles of these isoforms in vascular function are not known. It has been postulated that the α1-isoform serves a “housekeeping” role, whereas the α2-isoform localizes to a subsarcolemmal compartment and modulates contractility. To test this hypothesis, isoform-specific gene-targeted mice in which the mRNA for either the α1- or the α2-Na+/K+-ATPase isoform was ablated were utilized. Both of these knockouts, [Formula: see text] and [Formula: see text], are lethal; the latter dies at birth, which allows this neonatal aorta to be studied. Isometric force in [Formula: see text]-aorta was more sensitive to contractile agonists and less sensitive to the vasodilators forskolin and sodium nitroprusside (SNP) than wild-type (WT) aorta; [Formula: see text]-aortas had intermediate values. In contrast, neonatal [Formula: see text]-aorta was similar to WT. Western blot analysis indicated a population of 70% α1- and 30% α2-isoforms in the WT. Thus in terms of the total Na+/K+-ATPase protein, the [Formula: see text]-aorta (at 70%) would be similar to the [Formula: see text]-aorta (at 65%) but with a dramatically different phenotype. These data suggest that individual α-isoforms of the Na+/K+-ATPase differ functionally and that the α2-isoform couples more strongly to activation-relaxation pathways. Three-dimensional image-acquisition and deconvolution analyses suggest that the α2-isoform is distributed differently than the α1-isoform. Importantly, these isoforms do not localize to the same regions.