On the existence of a Na+-Ca2+ exchange system in the cell membrane of vascular smooth muscle.
Ca2+ uptake was studied in Na+-loaded cell membrane vesicles isolated from blood vessels of several species. A rapid uptake of Ca2+ was observed in an isotonic KCl medium when there was an outwardly directed Na+ concentration gradient created across the membrane. Elimination of the Na+ concentration gradient by including Na+ or the sodium ionophore monensin in the assay medium resulted in drastic reduction of Ca2+ uptake in the vesicles. This Ca2+ uptake was found to be specific for Na+ since other monovalent cations did not substitute Na+. Employing this approach, a Na+-Ca2+ exchange system was demonstrated in dog mesenteric artery, rat mesenteric artery, rat aorta, and rabbit aorta. The apparent Km for free Ca2+ of this process in these smooth muscles varies from 1.61 to 2.72 microM and the apparent maximum velocity varies from 7 to 16 nmol/min/mg protein. The results of the study with isolated membrane vesicles indicate the existence of a Na+-Ca2+ exchange in the cell membrane of vascular smooth muscle.
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Department of Pharmacology and Cell Biophysics, University of Cincinnati College of Medicine, OH 45267-0575.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004285:Dogs; D005260:Female; D066298:In Vitro Techniques; D007474:Ion Exchange; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000378:metabolism* / Q000648:ultrastructure; D051381:Rats; D011919:Rats, Inbred Strains; D012508:Sarcolemma / Q000187:drug effects / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D013997:Time Factors
D012964:Sodium; D002118:Calcium