Figure 5.

Effect of palmitoylation on NCX1 inactivation by Ca depletion and excess. Stably transfected FT-293 cells expressing WT and C739A NCX1 were voltage clamped in the whole-cell mode. Current traces are shown in red, capacitance traces in blue, and changes in extracellular Ca indicated in green. Outward NCX1 currents were activated by stepping extracellular Ca from 0 to 4 mM in cells expressing WT (left) and C739A exchangers (center). A) Effect of removal of intracellular Ca with EGTA. NCX1 inactivation is significantly slower in C739A NCX1 compared with WT: 240 s after application of EGTA a significantly greater current remains in cells expressing C739A NCX1 (right). *P < 0.05 vs. WT. B) Effect of PIP₂ depletion by a large Ca transient in the absence of intracellular ATP. In this protocol, the magnitude of the initial NCX1 current remains stable for periods of many minutes although the cytoplasmic ATP concentration is nominally zero. The initial activation cycle results in complete NCX1 inactivation in WT but not C739A-expressing cells (right). **P < 0.01 vs. WT.