Effects of the phospholipase inhibitor mepacrine on injury in ischemic and metabolically inhibited adult isolated myocytes. The phospholipase inhibitor mepacrine has been shown to delay cell death of metabolically inhibited cultured cardiomyocytes. The present study was initiated to determine if mepacrine also delays cell death and development of osmotic fragility of both metabolically inhibited and ischemic adult rat cardiomyocytes. Isolated myocyte suspensions were incubated with 3 mmol/l (millimolar) iodoacetic acid and 6 mmol/l amytal (inhibited) or were pelleted into a slurry and layered with oil (ischemic) in the presence and absence of 10 or 50 mumol/l (micromolar) mepacrine. Rates of contracture, cell viability as determined by trypan blue permeability, cell viability after osmotic swelling in 170 mOsm media (osmotic fragility), and cell morphology were monitored. Mepacrine had no effects on rates of contracture, but was found to significantly delay cell death during isotonic incubations of both metabolically inhibited and ischemic cells. In contrast, mepacrine had no effect on the development of osmotic fragility. Incubation of metabolically inhibited myocytes in calcium-free media did not delay contracture or cell injury, but did attenuate the protective effects of mepacrine. This study confirms previous reports that mepacrine protects cells from injury, extends the observations of protection to ischemic isolated adult myocytes, but shows that development of osmotic fragility is not inhibited by mepacrine. 