The role of phospholipase A2 in calcium-induced damage in cardiac and skeletal muscle.

This study compares the action of inhibitors of the eicosanoid cascade on calcium-induced myofilament damage in cardiac muscle of the perfused frog heart and incubated frog ventricle slices, and in skeletal muscle of incubated mammalian diaphragm and isolated and saponin-skinned amphibian pectoris cutaneous muscle. Mepacrine (10(-5) M) and indomethacin (3 x 10(-6) M) protected completely against myofilament damage induced by entry of calcium in the 'calcium-paradox' in frog heart. However, inhibition of phospholipase A2 (PLA2) (with chlorpromazine, 2 x 10(-4) M, or mepacrine, 10(-5) M, 5 x 10(-5) M), of cyclo-oxygenase enzymes (with indomethacin, 3 x 10(-6) M to 10(-5) M or BW755C, 3.8 x 10(-4) M), or of lipoxygenase enzymes (with BW755C, 3.8 x 10(-4) M or nordihydroguaiaretic acid, 2 x 10(-6) M or 5 x 10(-6) M) all failed in intact cardiac or skeletal muscle cells to prevent the myofilament damage that is rapidly triggered by 10(-2) M caffeine, 6 x 10(-6) M ruthenium red, 10(-4) M DNP or 5 micrograms ml-1 A23187. These agents also failed completely to protect against myofilament damage in saponin-skinned amphibian skeletal muscle when [Ca]i was raised to 8 x 10(-6) M. Thus, inhibition of PLA2 does not protect the myofilament apparatus against calcium released intracellularly, and it is suggested that mepacrine and indomethacin can block entry of calcium in the calcium-paradox in the amphibian heart. Chlorpromazine (2 x 10(-4) M) and mepacrine (10(-3) M) at zero [Ca] caused severe myofilament damage in skinned muscle, possibly due to an effect on membranes.(ABSTRACT TRUNCATED AT 250 WORDS)