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 Ca-45 uptake by 40% or more and reduced the half-maximal Na+ concentration for inhibition of Ca-45 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 P-32-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-45 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.