The Na+/Ca2+ antiporter in aortic smooth muscle cells. Characterization and demonstration of an activation by phorbol esters.
The Na+/Ca2+ antiporter is present in aortic smooth muscle cells of the A7r5 cell line. Imposing an outward Na+ gradient to the cells promoted a 45Ca2+ uptake component which was sensitive to amiloride derivatives and insensitive to blockers of the voltage-dependent Ca2+ channel. The Ca2+ uptake system was dependent on intracellular Na+ concentration; it was inactive when Li+ replaced intracellular Na+ and it was electrogenic. Flow cytometric analysis of cells that had been loaded with the Ca2+ indicator indo-1 showed that all conditions that promoted Ca2+ influx led to corresponding increases in the free cytoplasmic Ca2+ concentration. Treatment of the A7r5 cells with phorbol myristate acetate, a known activator of protein kinase C (Ca2+/phospholipid-dependent enzyme), led to a two-fold activation of the system and to larger intracellular Ca2+ transients when cells were shifted to Na+-free solutions. Activation was observed at all intracellular Na+ concentrations. Changing the activity of the Na+/Ca2+ system did not affect the size and duration of intracellular Ca2+ transients elicited by the Ca2+ mobilizing hormone vasopressin. It is concluded that the Na+/Ca2+ antiporter in smooth muscle cells is a target for protein kinase C but that the system is not involved in the regulation of Ca2+ transients induced by vasopressin.
Vigne
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Centre de Biochimie du Centre National de La Recherche Scientifique, Parc Valrose, Nice, France.
Breittmayer
J P
JP
Duval
D
D
Frelin
C
C
Lazdunski
M
M
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D004789:Enzyme Activation; D005453:Fluorescence; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D010703:Phorbol Esters / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D019831:Sodium-Calcium Exchanger; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014667:Vasopressins / Q000494:pharmacology
D002352:Carrier Proteins; D010703:Phorbol Esters; D019831:Sodium-Calcium Exchanger; D014667:Vasopressins; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium