The Na+/Ca2+ exchanger (NCX) in plasma membranes either moves Ca2+ 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 [Ca2+](i) elicited by reverse mode NCX activity. The elevation in [Ca2+](i) elicited by reverse mode NICX activity was significantly diminished by thapsigargin. KB-R7943 could only partially suppress the [Ca2+](i) change. Measurement of the [Ca2+](i) concurrent with reverse mode NCX current by perforated whole-cell patch showed that elevation in [Ca2+](i) but not the current, was inhibited by thapsigargin. The change in [Ca2+](i) response elicited by nicotinic acetylcholine receptor agonist was inhibited by thapsigargin. These suggest the importance of intracellular Ca2+ stores in facilitating the [Ca2+](i) elevation elicited by reverse mode NCX activity under physiological condition. (c) 2006 Elsevier Inc. All rights reserved.