Calcium elevation elicited by reverse mode Na+/Ca2+ exchange activity is facilitated by intracellular calcium stores in bovine chromaffin cells

The Na(+)/Ca(2+) exchanger (NCX) in plasma membranes either moves Ca(2+) out of (forward mode) or into (reverse mode) cells depending on the electrochemical gradient of these ions across the membrane. In this report, we characterize the sources responsible for the elevation in Ca(2+)](i) elicited by reverse mode NCX activity. The elevation in Ca(2+)](i) elicited by reverse mode NCX activity was significantly diminished by thapsigargin. KB-R7943 could only partially suppress the Ca(2+)](i) change. Measurement of the Ca(2+)](i) concurrent with reverse mode NCX current by perforated whole-cell patch showed that elevation in Ca(2+)](i), but not the current, was inhibited by thapsigargin. The change in Ca(2+)](i) response elicited by nicotinic acetylcholine receptor agonist was inhibited by thapsigargin. These suggest the importance of intracellular Ca(2+) stores in facilitating the Ca(2+)](i) elevation elicited by reverse mode NCX activity under physiological condition.