INTRAMITOCHONDRIAL CALCIUM AND MAGNESIUM LEVELS IN SKELETAL-MUSCLE SUBMITTED TO TOTAL OR PARTIAL LIMB ISCHEMIA

Skeletal muscle temperature and mitochondrial content of Ca2+ and Mg2+ were measured after 3 h of total or partial limb ischemia in male Wistar rats (250-350 g). The decreases in biceps muscle temperature, measured with a needle thermistor (4.4 +/- 0.26-degrees-C, mean +/- SEM (17 rats) and 6.3 +/- 0.26-degrees-C (31 rats) in partial ischemia (PI, aorta clamp) and total ischemia (TI, hind leg tourniquet), respectively) were consistent with the expected extent of blood flow reduction for the two ischemic conditions. Mitochondrial calcium levels increased after partial ischemia from 2.67 +/- 0.13 (46 rats) to 4.65 +/- 0.38 (12 rats) nmol/mg protein and increased to 7.87 +/- 0.68 (14 rats) after total ischemia (P < 0.05). In contrast, mitochondrial magnesium decreased after partial ischemia from 10.14 +/- 0.35 to 8.22 +/- 0.28 (13 rats) but increased in the mitochondria of muscle submitted to total ischemia to 12.0 +/- 0.80 (14 rats; P < 0.05). No changes were observed in the number of binding sites for safranine, which competes for calcium binding sites on the inner mitochondrial membrane (25.46 +/- 0.38 nmol/mg protein for sham (20 rats) and 25 +/- 0.68 (7 rats) for PI and 25 +/- 0.31 (5 rats) for TI). The data suggest that the greater resistance of rat muscle to total than to partial ischemia may be due at least in part to the increased mitochondrial Mg2+ content.