Sodium-calcium exchange and store-dependent calcium influx in transfected chinese hamster ovary cells expressing the bovine cardiac sodium-calcium exchanger. Acceleration of exchange activity in thapsigargin-treated cells.
The effects of extracellular Na+ on store-dependent Ca2+ influx were compared for transfected Chinese hamster ovary cells expressing the bovine cardiac Na+-Ca2+ exchanger (CK1.4 cells) and vector-transfected control cells. Store-dependent Ca2+ influx was elicited by depletion of intracellular Ca2+ stores with ionomycin, thapsigargin, or extracellular ATP, a purinergic agonist. In each case, the rise in [Ca2+]i upon the addition of extracellular Ca2+ was reduced in CK1.4 cells compared with control cells at physiological [Na+]o. When Li+ or NMDG was substituted for Na+, the CK1.4 cells showed a greater rise in [Ca2+]i than control cells over the subsequent 3 min after the addition of Ca2+o. Under Na+-free conditions, SK&F 96365 (50 microM), a blocker of store-operated Ca2+ channels, nearly abolished the thapsigargin-induced rise in [Ca2+]i in the control cells but only partially inhibited this response in the CK1.4 cells. We conclude that in the CK1.4 cells, Ca2+ entry through store-operated channels was counteracted by Na+o-dependent Ca2+ efflux at physiological [Na+]o, whereas Ca2+ entry was enhanced through Na+i-dependent Ca2+ influx in the Na+-free medium. We examined the effects of thapsigargin on Ba2+ entry in the CK1.4 cells because Ba2+ is transported by the Na+-Ca2+ exchanger, but it enters these cells only poorly through store-operated channels, and it is not sequestered by intracellular organelles. Thapsigargin treatment stimulated Ba2+ influx in a Na+-free medium, consistent with an acceleration of Ba2+ entry through the Na+-Ca2+ exchanger. We conclude that organellar Ca2+ release induces a regulatory activation of Na+-Ca2+ exchange activity.
Chernaya
G
G
Department of Physiology, University of Medicine and Dentistry of New Jersey, The New Jersey Medical School, Newark, 07103, USA.
Vázquez
M
M
Reeves
J P
JP
D000818:Animals; D001464:Barium / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002352:Carrier Proteins / Q000096:biosynthesis / Q000378:metabolism*; D002417:Cattle; D002999:Clone Cells; D006224:Cricetinae; D003470:Culture Media; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005822:Genetic Vectors; D007093:Imidazoles / Q000494:pharmacology; D007700:Kinetics; D009206:Myocardium / Q000378:metabolism*; D015388:Organelles / Q000378:metabolism; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D019831:Sodium-Calcium Exchanger; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D014162:Transfection
D002121:Calcium Channel Blockers; D002352:Carrier Proteins; D003470:Culture Media; D004791:Enzyme Inhibitors; D007093:Imidazoles; D011994:Recombinant Proteins; D019831:Sodium-Calcium Exchanger; D013729:Terpenes; D001464:Barium; D019284:Thapsigargin; D012964:Sodium; D000252:Calcium-Transporting ATPases; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole; D002118:Calcium