ATP-dependent regulation of sodium-calcium exchange in Chinese hamster ovary cells transfected with the bovine cardiac sodium-calcium exchanger.
Chinese hamster ovary cells expressing the bovine cardiac Na/Ca exchanger were treated with ouabain to increase [Na+]i and stimulate Ca2+ influx by Na/Ca exchange. Depletion of cellular ATP inhibited 45Ca uptake by 40% or more and reduced the half-maximal Na+ concentration for inhibition of 45Ca uptake from 90 to 55 mM. ATP depletion also reduced the rate of rise in [Ca2+]i when [Na+]o was reduced and inhibited the decline in [Ca2+]i when high [Na+]o was restored. The effects of ATP depletion were either absent or reduced in cells expressing a mutant exchanger missing most of the cytosolic hydrophilic domain. We were unable to detect a phosphorylated form of the exchanger in immunoprecipitates from 32P-labeled cells. ATP depletion caused a breakdown in the actin cytoskeleton of the cells. Treatment of the cells with cytochalasin D mimicked the effects of ATP depletion on the [Na+] inhibition profile for 45Ca uptake. Thus, ATP depletion inhibits both the Ca2+ influx and Ca2+ efflux modes of Na/Ca exchange, and may alter the competitive interactions of extracellular Na+ and Ca2+ with the transporter. The latter effect appears to be related to changes in the actin cytoskeleton.
Condrescu
M
M
Department of Physiology, University of Medicine and Dentistry-New Jersey Medical School, Newark 07103, USA.
Gardner
J P
JP
Chernaya
G
G
Aceto
J F
JF
Kroupis
C
C
Reeves
J P
JP
D000199:Actins / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000502:physiology*; D000818:Animals; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000502:physiology*; D002417:Cattle; D006224:Cricetinae; D015638:Cytochalasin D / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D009206:Myocardium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger; D014162:Transfection
D000199:Actins; D002352:Carrier Proteins; D019831:Sodium-Calcium Exchanger; D015638:Cytochalasin D; D000255:Adenosine Triphosphate; D012964:Sodium; D002118:Calcium