The Cardiac Sodium‐Calcium Exchanger Associates with Caveolin‐3

Abstract

The cardiac Na/Ca exchanger's (NCX1) role in calcium homeostasis during myocardial contractility makes it a possible target of signaling factors regulating inotropy. Caveolae, structured invaginations of the plasmalemma, are known to concentrate a wide variety of signaling factors. The predominant coat proteins of caveolae, caveolins, dock to and regulate the activity of these signaling factors and other proteins through interaction with their scaffolding domain. In this study we investigated the interaction of NCX1 with caveolin proteins. Western blots of bovine cardiac sarcolemmal vesicles revealed the presence of caveolin‐1, ‐2, and ‐3. Immunoprecipitation of detergent‐solubilized vesicle proteins with either NCX1 or caveolin‐3 antibodies indicated that NCX1 coprecipitates with caveolin‐3, but not with caveolin‐1 and ‐2. Functional disruption of caveolae, by β‐cyclodextrin treatment of vesicles, diminished coprecipitation of caveolin‐3 and NCX1 activity. NCX1 has five potential caveolin‐binding motifs, two of which are in the transporter's exchange inhibitory peptide (XIP) domain. The presence of 50 mM XIP peptide enhanced coprecipitation of caveolin‐3 with NCX1 independent of calcium concentration. We conclude that NCX1 associates specifically with caveolin‐3. Partitioning of NCX1 in caveolae has implications for temporal and spatial regulation of excitation‐contraction and ‐relaxation coupling in cardiac myocytes.

Targeting and Stability of Na/Ca Exchanger 1 in Cardiomyocytes Requires Direct Interaction with the Membrane Adaptor Ankyrin-B

“…Additionally, calcineurin, 14-3-3⑀ and F-actin have been shown to associate with the Na/Ca exchanger and modulate its activity (56 -58). Finally, both caveolin 3 and annexin A5 may also associate with Na/Ca exchanger in vivo (59,60). Although it is likely that one or more of these proteins may influence the cellular pathways responsible for the localization and stability of Na/Ca exchanger in cardiomyocytes, in vivo data to support the physiological relevance of these interactions is not yet available.…”

Caveolinopathies: from the biology of caveolin-3 to human diseases

“…[14][15][16][17] In cardiomyocites, the ion channels HCN4, Ca v 1.2, K v 1.5, kir6.2/Sur2a, Na v 1.5, and NCX are targeted to caveolae, and Cav-3 directly interacts with b 2 -adrenoreceptors with whom it regulates the sarcolemmal targeting of cyclic AMP signal. [18][19][20][21][22] Notably, chemical disruption of caveolae affects the excitation-contraction coupling and b-adrenergic responsiveness of adult cardiac myocites. 21,22 Likewise, Cav-3 has a role in the regulation of energy metabolism of muscle cells.…”

Cardiac Sodium-Calcium Exchanger Is Regulated by Allosteric Calcium and Exchanger Inhibitory Peptide at Distinct Sites

“…The cardiac NCX associates with caveolin-3, and caveolin-binding motifs are located in the endogenous XIP region (residues 223-231), but also within the herein identified XIP-regulatory domain (residues 620 -627). 31 It was suggested that by its association with the endogenous XIP region (or possibly also its regulatory domain), caveolin-3 may activate the NCX by inhibiting the interaction of the endogenous XIP region with its binding site. 31 If this holds true, then higher membrane content of caveolin-3 in cardiac myocytes may reduce the inhibitory efficacy of exogenous XIP compared with HEK cells, where caveolin-3 is virtually absent.…”

“…31 It was suggested that by its association with the endogenous XIP region (or possibly also its regulatory domain), caveolin-3 may activate the NCX by inhibiting the interaction of the endogenous XIP region with its binding site. 31 If this holds true, then higher membrane content of caveolin-3 in cardiac myocytes may reduce the inhibitory efficacy of exogenous XIP compared with HEK cells, where caveolin-3 is virtually absent. 32 In a similar way, ATP-and PIP 2 -induced activation of I NCX are supposedly attributable to interaction of PIP 2 with the endogenous XIP region, thus inhibiting its interaction with the XIP regulatory site.…”