The effects of varying temperatures from 25 degrees to 37 degrees C on calcium binding characteristics of sarcoplasmic reticulum from malignant hyperthermia-susceptible (MHS) and control pig muscle were examined. Two groups of MHS pigs were included: those with high susceptibility to malignant hyperthermia (MHS group) and a cross-bred, less susceptible group (MHX). At 25 degrees C, calcium binding was lower for MHS than for controls and MHX. As temperature was increased by 2 degrees C jumps, calcium binding decreased in all sarcoplasmic reticulum fractions. At 35 degrees C a sharp decrease in calcium binding occurred in the MHS and MHX fractions. The sharp decrease in calcium binding at 35 degrees C differentiated the MHS and MHX fractions from controls. The initial velocity (Vi) for calcium binding was lower in MHS fractions between 25 degrees and 35 degrees C when compared with MHX and controls. All fractions had increased Vi values as temperature increased from 25 degrees to 35 degrees C. From 35 degrees to 39 degrees Vi for controls increased markedly. In contrast, Vi for the MHX fraction decreased as temperature exceeded 35 degrees C. These temperature effects on calcium binding characteristics of sarcoplasmic reticulum from MHS and MHX muscle may be indicative of a membrane transition that impairs calcium binding.
T E Nelson, D E Bee