Calcium and magnesium content of skeletal muscle. Studies in subjects undergoing diagnostic testing for malignant hyperthermia.

Ca2+ and Mg2+ contents were measured and compared among three different malignant hyperthermia susceptible (MHS) diagnostic groups. No difference was found among mean values for Ca2+ content, whereas Mg2+ content was greater in MHS muscle. Variance of measured values was unequal and greatest among MHS muscles, suggesting a possible abnormal distribution associated with MHS. Although more muscle fibres with Ca2+ less than or equal to 12 mumol g-1 were observed in MHS muscle, this difference was not statistically significant. In contrast, non-parametric analysis showed that the population of Mg2+ values was significantly greater in the MHS muscle. This study suggests that the distribution of Ca2+ and Mg2+ values is different in MHS muscle as a result of unknown genetic factors associated with the disease.

Comparison of Ca++ uptake and spontaneous Ca++ release from sarcoplasmic reticulum vesicles isolated from muscle of malignant hyperthermia diagnostic patients.

Inward Ca++ transport and spontaneous Ca++ release activities were compared among sarcoplasmic reticulum (SR) membrane fractions isolated from human skeletal muscle in patients undergoing malignant hyperthermia (MH) diagnostic contracture testing. Two different membrane fractions were isolated, a heavy (8-12,000 X g) and light (12-48,000 X g) fraction, from each diagnostic subject. The rates of inward Ca++ transport were faster in light SR compared to heavy SR, but no statistically significant difference was observed among MH diagnostic groups. Spontaneous Ca++ release occurred at optimum Ca++ preload in all SR fractions and this preload did not differ among MH diagnostic groups. Optimal Ca++ preload for rate of spontaneously released Ca++ was greater in light SR compared to heavy SR. Similarly, rate of Ca++ release was faster in light SR than in heavy SR, but no difference in rate of spontaneously released Ca++ was observed among MH diagnostic groups. Amount of Ca++ released did not differ among SR fractions and it did not differ among diagnostic groups. In contrast to previous studies showing a defect in Ca++-induced Ca++ release, the mechanisms related to spontaneous Ca++ release and to oxalate-facilitated inward Ca++ transport, as measured in this study, appear to be normal in SR from human MH skeletal muscle.