Na⁺-K⁺-ATPase and Ca²⁺clearance proteins in smooth muscle: a functional unit

Abstract

The Na(+)-K(+)-ATPase (NKA) can affect intracellular Ca(2+) concentration regulation via coupling to the Na(+)-Ca(2+) exchanger and may be important in myogenic tone. We previously reported that in mice carrying a transgene for the NKA alpha(2)-isoform in smooth muscle (alpha(2sm+)), the alpha(2)-isoform protein as well as the alpha(1)-isoform (not contained in the transgene) increased to similar degrees (2-7-fold). Aortas from alpha(2sm+) mice relaxed faster from a KCl-induced contraction, hypothesized to be related to more rapid Ca(2+) clearance. To elucidate the mechanisms underlying this faster relaxation, we therefore measured the expression and distribution of proteins involved in Ca(2+) clearance. Na(+)-Ca(2+) exchanger, sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA), and plasma membrane Ca(2+)-ATPase (PMCA) proteins were all elevated up to approximately fivefold, whereas actin, myosin light chain, and calponin proteins were not changed in smooth muscle from alpha(2sm+) mice. Interestingly, the corresponding Ca(2+) clearance mRNA levels were unchanged. Immunocytochemical data indicate that the Ca(2+) clearance proteins are distributed similarly in wild-type and alpha(2sm+) aorta cells. In studies measuring relaxation half-times from a KCl-induced contraction in the presence of pharmacological inhibitors of SERCA and PMCA, we estimated that together these proteins were responsible for approximately 60-70% of relaxation in aorta. Moreover, the percent contribution of SERCA and PMCA to relaxation rates in alpha(2sm+) aorta was not significantly different from that in wild-type aorta. The coordinate expressions of NKA and Ca(2+) clearance proteins without change in the relative contributions of each individual protein to smooth muscle function suggest that NKA may be but one component of a larger functional Ca(2+) clearance system.

Nanomolar ouabain increases NCX1 expression and enhances Ca2+signaling in human arterial myocytes: a mechanism that links salt to increased vascular resistance?

“…These Na ϩ and Ca 2ϩ transporter protein distribution patterns are very similar to those in rodent arterial myocytes and some other cell types (26,31,39,46,48,54). The implication of this structural organization, consisting of units (plasmerosomes) of PM microdomains closely opposed to junctional SR, is that the ␣ 2 -Na ϩ pumps, NCX1 and ROCs (of which TRPC6 proteins are components), and the SR are also functionally linked (8).…”

Arterial α2-Na+pump expression influences blood pressure: lessons from novel, genetically engineered smooth muscle-specific α2mice

“…␣ 1 -Na ϩ pump, NCX1, SERCA2, and PMCA proteins were all upregulated in both the aorta and gastric antrum. Contraction-related proteins (actin and 20-kDa myosin light chain) were, however, unaffected (42,43).…”

“…Prior immunoblot studies (42,43) of the aorta and gastric antrum in ␣ 2 SM-Tg mice revealed that not only the ␣ 2 -Na ϩ pumps but also other Na ϩ and Ca 2ϩ transporters were affected in these SM-containing tissues. ␣ 1 -Na ϩ pump, NCX1, SERCA2, and PMCA proteins were all upregulated in both the aorta and gastric antrum.…”

“…␣ 1 -Pumps ("housekeepers") maintain the low intracellular Na ϩ concentration in most of the cytoplasm (1). The more sparse ␣ 2 -pumps colocalize with plasma membrane (PM) Na ϩ /Ca 2ϩ exchanger 1 (NCX1) and sarcoplasmic reticulum (SR) Ca 2ϩ pumps [sarco(endo)plasmic reticulum Ca 2ϩ -ATPase 2 (SERCA2)] at PM-SR junctions in ASMCs (21,28,42,51). As a result, the functional coupling of these transporters helps regulate local cytosolic Na ϩ and Ca 2ϩ concentrations and Ca 2ϩ signaling (1,25,31,40,42).…”

The Plasma Membrane Calcium ATPasesand Their Role as Major New Players in Human Disease

“…In contrast to cardiac muscle, it has been demonstrated that the PMCA accounts for the bulk of Ca 2ϩ extrusion from vascular smooth muscle, and its inhibition prolongs aortic relaxation to a similar extent to that of SERCA while NCX inhibition has little effect (298), and in myometrial resistance arteries PMCA inhibition mimics the phenotype of preeclamptic vessels (398). As described in section IIIA, PMCA1 has been identified in numerous studies as a leading candidate gene for the development of hypertension.…”