Cross talk between plasma membrane Na(+)/Ca (2+) exchanger-1 and TRPC/Orai-containing channels: key players in arterial hypertension

Abstract

Arterial smooth muscle (ASM) Na(+)/Ca(2+) exchanger type 1 (NCX1) and TRPC/Orai-containing receptor/store-operated cation channels (ROC/SOC) are clustered with α2 Na(+) pumps in plasma membrane microdomains adjacent to the underlying junctional sarcoplasmic reticulum. This arrangement enables these transport proteins to function as integrated units to help regulate local Na(+) metabolism, Ca(2+) signaling, and arterial tone. They thus influence vascular resistance and blood pressure (BP). For instance, upregulation of NCX1 and TRPC6 has been implicated in the pathogenesis of high BP in several models of essential hypertension. The models include ouabain-induced hypertensive rats, Milan hypertensive rats, and Dahl salt-sensitive hypertensive rats, all of which exhibit elevated plasma ouabain levels. We suggest that these molecular mechanisms are key contributors to the increased vascular resistance ("whole body autoregulation") that elevates BP in essential hypertension. Enhanced expression and function of ASM NCX1 and TRPC/Orai1-containing channels in hypertension implies that these proteins are potential targets for pharmacological intervention.

Figure 1. Immunofluorescent localization of NCX1 and Orai1 in hASMC

a and b: images of cell double labeled with anti-NCX1 antibody (a) and anti-Orai1 antibody (b). Insets in a and b (enlargements of the boxed areas) indicate that NCX1 and Orai1 labels show similar distributions. Panels ci and cii are pseudocolor images (green – anti-NCX1; red – anti-Orai1) of enlarged boxes from a and b, respectively. Panel ciii: colocalization of NCX1 (ci) and Orai1 staining (cii); the yellow, orange and yellow/green areas in the overlay indicate regions of overlap between the two epitopes. Reprinted with permission from (Baryshnikov et al. 2009).

Figure 2. Up-regulated NCX1 and TRPC6 in de-endothelialized mesenteric arteries from hypertensive Dahl salt-sensitive (DS) rats on high salt (HS) diet

a. Development of hypertension in DS rats on HS diet. Normotensive male DS rats were split into 2 groups; one was fed normal salt (NS) and the other, HS (6%) diet. A HS diet for 12 days markedly increases BP in DS rats (Student’s t-test, * = P<0.05). b and c: Western blot analysis of NCX1 (b) and TRPC6 (c) expression in mesenteric artery from DS rats on NS and HS diets. Representative Western blots are shown (30 μg/lane); comparable results were obtained in 4 immunoblots.

Figure 3

Augmented NCX1 expression and enhanced Ca²⁺ entry via the reverse mode of NCX1 in freshly dissociated mesenteric artery myocytes from Milan hypertensive strain (MHS) rats. a and b. Western blot analysis of NCX1 protein expression in smooth muscle cell membranes from mesenteric arteries of MNS and MHS rats. a. Representative immunoblot (30 μg/lane). b. Summary data are normalized to the amount of β-actin and are expressed as mean ± S.E.M. from 9 immunoblots (total of 22 rats). ***P<0.001 vs. MNS arterial SMCs. c, d. Activation of the reverse mode of NCX1 in arterial ASMCs from MNS (black) and MHS (grey) rats. a. Representative time course records showing changes in [Ca²⁺]_cyt in single arterial SMCs; time of treatment with Na⁺-free solution is indicated. Nifedipine (10 μM) was added 10 min before the records shown, and was maintained throughout the experiment. b. Summarized data show the NCX1-mediated Ca²⁺ entry in 33 MNS and 23 MHS mesenteric artery SMCs. *P<0.05 vs. MNS arterial myocytes. Reprinted with permission from (Zulian et al. 2010).