Composite results of experiments characterizing MEND in five protocols. Bar graphs represent the peak Cm occurring in an experiment, during or shortly after a Ca transient, in relation to Cm after the occurrence of MEND. Each dataset reflects five or more observations. (A) MEND occurring with the indicated cytoplasmic ATP concentrations in response to a single Ca influx episode of 12–16 s. (B) MEND occurring upon pipette perfusion of an NTA-buffered solution with 0.2 mM of free Ca. (C) MEND occurring upon pipette perfusion of 2 mM ATP and 0.2 mM GTP after the cells were opened and maintained without nucleotides for 3 min and exposed to one Ca influx episode for 2 s. (D) MEND occurring during a single Ca influx episode for 15 s in the presence of cytoplasmic spermidine (1 mM). (E) MEND occurring over two Ca influx episodes of 15-s duration, separated by 2 min, in the presence of cytoplasmic spermidine (1 mM). See Results for complete details.