Na+-Ca2+ exchange and Ca2+ efflux in transfected Chinese hamster ovary cells
Na+-Ca2+ exchange and Ca2+ efflux in transfected Chinese hamster ovary cells
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DOI：
10.1054/ceca.1999.0046
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发表时间：
1999-07-01
期刊：
影响因子：
4
通讯作者：
Reeves, JP
中科院分区：
文献类型：
--
作者：
Fang, Y;Condrescu, M;Reeves, JP
The objective of this study was to assess the contribution of Na+-Ca2+ exchange activity to Ca2+ efflux at various cytosolic Ca2+ concentrations ([Ca2+](i)) in transfected Chinese hamster cells expressing the bovine cardiac Na+-Ca2+ exchanger. Ionomycin was added to fura-2 loaded cells and the resulting [Ca2+](i) transient was monitored in Ca2+-free media with or without extracellular Na+. The presence of Na+ reduced both the amplitude and duration of the [Ca2+](i) transient. Na+ had similar effects when the peak of the [Ca2+](i) transient was buffered to 100 nM by cytosolic EGTA, or when Ca2+ was slowly released from internal stores with thapsigargin. Ca2+ efflux following ionomycin addition was directly measured with extracellular fura-2 and followed a biphasic time course (t(1/2) approximate to 10 s and 90 s). The proportion of total efflux owing to the rapid phase was increased by Na+ and reduced by EGTA-loading. Na+ accelerated the initial rate of Ca2+ efflux by 65% in unloaded cells but only by 16% in EGTA-loaded cells. In both cases, the stimulation by Na+ was less than expected, given the pronounced effects of Na+ on the [Ca2+](i) transient. We conclude that the exchanger contributes importantly to Ca2+ efflux activity at all [Ca2+](i) values above 40 nM. We also suggest that Ca2+ efflux pathways may involve non-cytosolic or local routes of Ca2+ traffic. (C) Harcourt Publishers Ltd 1999.
