C6TPP currents are nearly unaffected by Ca-induced MEND. 0.3 mM C6TPP is applied briefly multiple times in each experiment, as indicated. (A) 2 mM of the polyamine, EDA, is included in both the cytoplasmic and extracellular solutions to promote rapid MEND (50% in 5 s) during Ca influx by NCX1. Thereafter, C6TPP current is decreased by 12% on average. DSF, 50. (B) Composite results for four experiments similar to A. Ca-activated MEND causes a 50% loss of C_m, whereas C12TPP currents decrease by just 10%. (C) Using a cytoplasmic solution with 6 mM ATP and no polyamine, Ca influx by NCX1 is activated four times. C_m decreases substantially in a delayed fashion after each of the Ca influx episodes, resulting finally in a 45% decrease of C_m. 0.3-mM C6TPP currents are unchanged. DSF, 41.