Immunofluorescence localization of the Na-Ca exchanger in heart cells

Abstract

We investigated the localization of the Na-Ca exchanger in fixed, isolated heart cells from rat and guinea pig using immunocytochemical methods with epifluorescence and confocal microscopy. We found that the Na-Ca exchanger is distributed throughout all membranes in contact with the extracellular space, including the sarcolemma, the transverse tubules (T-tubules), and the intercalated disks. Microscopic nonuniformities in the fluorescent labeling appear to reflect varying views of the membranes containing Na-Ca exchanger protein. Confocal thin-section imaging reveals a regular grid of discrete foci of fluorescence, which represent Na-Ca exchanger in T-tubules viewed en face. These foci are 1.80 +/- 0.01 microns apart from sarcomere to sarcomere and are aligned with the Z-line. Along each Z-line, these foci are spaced at 1.22 +/- 0.11-microns intervals. Longitudinal sections of the sarcolemma-T-tubule junction show a comblike appearance, with T-tubules extending inward from the heavily labeled sarcolemma. Our finding that the Na-Ca exchanger is widely distributed over the cell surface may provide further insight into the role of Na-Ca exchange in the heart.

Sodium/Calcium Exchanger (NCX1) Macromolecular Complex

“…NCX1 was identified in the sarcolemmal membrane and in the Z-lines of cardiomyocytes (Fig. 5) as already reported (48,49). Interestingly, mAKAP is also localized in the Z-lines and the dual staining of NCX1 and mAKAP confirmed that both of these proteins are present in the same location in rat cardiomyocytes (Fig.…”

“…There is also the possibility that AKAPs can directly bind to the cytoskeleton as was demonstrated for ezrin (68). Colocalization of NCX1 with mAKAP and PKA-RI-NCX1 has been identified in the sarcolemma and in Z-line/T-tubules by us and others (48,49,67). The mAKAP has been localized in the sarcoplasmic reticulum, in the perinuclear region, and in Z-line/T-tubular regions in cells (37,47,69).…”

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

“…Normal function of the Na/Ca exchanger requires proper biophysical properties and precise localization at excitable cardiac membranes including the sarcolemma and cardiomyocyte transverse-tubule surfaces (5)(6)(7)(8)(9). Whereas the biophysical features of the cardiac Na/Ca exchanger are widely studied and well defined (10 -13), the molecular mechanisms required for the targeting and retention of the Na/Ca exchanger at specialized membrane domains in cardiomyocytes are unknown.…”

Ca2+‐ATPase distributes differently in cardiac sarcolemma than dihydropyridine receptor α1 subunit and Na+/Ca2+ exchanger

“…Using these incompletely fractionated cardiac membranes and radiolabeled DHPs, cardiac DHP receptors were suggested to be localized at surface sarcolemma and T-tubules [ 11,141. The cardiac Na+/Ca'+ exchanger, on the other hand, has recently been immnohistochemically localized to surface sarcolemma as well as T-tubules in guinea pig and rat heart [15,16].…”