Subcellular localization of the Na⁺/H⁺exchanger NHE1 in rat myocardium

Abstract

The Na+/H+exchanger NHE1 isoform is an integral component of cardiac intracellular pH homeostasis that is critically important for myocardial contractility. To gain further insight into its physiological significance, we determined its cellular distribution in adult rat heart by using immunohistochemistry and confocal microscopy. NHE1 was localized predominantly at the intercalated disk regions in close proximity to the gap junction protein connexin 43 of atrial and ventricular muscle cells. Significant labeling of NHE1 was also observed along the transverse tubular systems, but not the lateral sarcolemmal membranes, of both cell types. In contrast, the Na+-K+-ATPase α1-subunit was readily labeled by a specific mouse monoclonal antibody (McK1) along the entire ventricular sarcolemma and intercalated disks and, to a lesser extent, in the transverse tubules. These results indicate that NHE1 has a distinct distribution in heart and may fulfill specialized roles by selectively regulating the pH microenvironment of pH-sensitive proteins at the intercalated disks (e.g., connexin 43) and near the cytosolic surface of sarcoplasmic reticulum cisternae (e.g., ryanodine receptor), thereby influencing impulse conduction and excitation-contraction coupling.

Localized Na+/H+ Exchanger 1 Expression Protects Ca2+-regulated Adenylyl Cyclases from Changes in Intracellular pH

“…Studies in rat myocardium support the theory that specific targeting of NHE1 can create microenvironments for pH-sensitive proteins (e.g. connexin 43 and ryanodine receptor) (50). However, we propose that the targeting of NHE1 to caveolae serves to protect pHsensitive proteins (e.g.…”

“…As with AC8, the Ca 2ϩ regulation of AC6 was enhanced at pH 7.85 and reduced at pH 7.14 compared with controls (pH 7.50). The corresponding IC 50 values for Ca 2ϩ were 0.19, 0.33, and 1.10 M at pH 7.85, 7.50, and 7.14, respectively (Fig. 1B).…”

Traditional and emerging roles for the SLC9 Na+/H+ exchangers

“…It resides almost exclusively at the surface of cells, but preferentially accumulates in discrete microdomains within the plasma membrane, depending on type and state of the cell. In polarized epithelial cells, NHE1 localizes to the basolateral membrane, in cardiac myocytes to intercalated disks and T-tubulues and in resting fibroblasts to sites of focal adhesions [55,134,16].…”

On-chip acidification rate measurements from single cardiac cells confined in sub-nanoliter volumes

“…6). Furthermore, the Na+ /H+ exchanger is localized at the intercalated disks (faces of the brick shaped cardiac myocytes) and the transverse tubules (Petrecca et al, 1999). The tubules are hollow vessels perpendicular to the longitudinal surface and occupy a 64% of the total surface membrane (Soeller and Cannell, 1999) leaving only approximately 2% for the intercalated disk facing quasi-reference electrode.…”