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 ] and stimulate Ca influx by Na/Ca exchange. Depletion of cellular ATP inhibited Ca uptake by 40% or more and reduced the half-maximal Na concentration for inhibition of Ca uptake from 90 to 55 m M . ATP depletion also reduced the rate of rise in [Ca ] when [Na ] was reduced and inhibited the decline in [Ca ] when high [Na ] 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 P-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 Ca uptake. Thus, ATP depletion inhibits both the Ca influx and Ca efflux modes of Na/Ca exchange, and may alter the competitive interactions of extracellular Na and Ca with the transporter. The latter effect appears to be related to changes in the actin cytoskeleton.