Table 3.

Effect of calpain inhibitor PD150606 (100 μM) on poststress TMRM fluorescence and survival

TMRM Fluorescence 5 h post-stress, % no-stress control
Stress alone	Stress + PD150606 pretreat
12.5 ± 1.8 (12)	24.9 ± 2.6* (12)

Cell survival, %
Stress alone	Stress + PD150606 pretreat	Stress + PD150606 stress onset
26 ± 3	50 ± 3*	52.5 ± 4*

Values are means ± SE, with number of culture wells shown in parentheses. Pretreat indicates that PD150606 was present 2 h before, during, and after the stress; stress onset indicates drug presence during and after the stress. TMRM fluorescence was measured 5 h post-stress (high-[K⁺] medium throughout). Cell survival was measured 24 h post-stress (live/dead assay, see materials and methods).

^*P < 0.001 compared with cultures stressed without drug. The protection afforded by PD150606 did not extend to 48 h post-stress, when survival measured in both PD150606-treated and nontreated cultures was similar (18-21%), a result repeated in 2 additional experiments. Long-term exposure to this drug may itself be toxic, because in nonheated cultures a 48-h exposure to PD150606 reduced survival from 90 to 39.5% as measured by propidium iodide exclusion.