Na(+)-Ca2+ exchanger in arteries: identification by immunoblotting and immunofluorescence microscopy

Abstract

Antibodies raised against dog cardiac Na(+)-Ca2+ exchanger were employed to determine the presence and distribution of the exchanger in arterial smooth muscle (ASM) cells. The antiserum cross-reacted with protein bands of approximately 70, 120, and 150-160 kDa from the membranes of ASM cells, as well as heart sarcolemma. A cardiac Na(+)-Ca2+ exchanger cDNA probe hybridized to 7-kilobase (kb) mRNA from myocytes of the mesenteric artery. Thus ASM cells possess a "cardiac type" Na(+)-Ca2+ exchanger. The relative amounts of 7-kb mRNA and antigen detected on Northern and Western blots, respectively, however, indicate that vascular myocytes contain much less of this transporter than do cardiac myocytes. Immunofluorescence studies on cultured arterial myocytes suggest that the exchanger molecules are organized in reticular patterns over the cell surfaces. A similar pattern is observed when cells are stained for sarcoplasmic reticulum (SR) Ca(2+)-ATPase. This raises the possibility that the exchanger in the plasmalemma of arterial myocytes may be associated, perhaps functionally as well as structurally, with the underlying SR. The antiserum also cross-reacted with endothelial cell membranes, but labeling was lighter and more diffuse than in the myocytes.