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1 Department of Physiology, McGill University, Montreal, Quebec, Canada H3G 1Y6; and 2 Division of Cell Biology, Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8
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
1-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.
ion transporters; pH regulation; subcellular; confocal microscopy
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