Fura-2 detected myoplasmic calcium and its correlation with contracture force in skeletal muscle from normal and malignant hyperthermia susceptible pigs

Fura-2 was used to estimate myoplasmic [Ca²⁺] in intact intercostal muscle fibers from normal and malignant hyperthermia susceptible (MHS) pigs. Small muscle bundles (20–50 fibers) were loaded with the membrane-permeant form of the dye. Resting myoplasmic [Ca²⁺] were not significantly different in normal and MHS muscles. Halothane produced increases in myoplasmic Ca²⁺ with associated contractures in MHS muscles, but not in normal muscles. These halothane effects were reversible. Caffeine produced increases in myoplasmic Ca²⁺ and contractures in both MHS and normal muscles. The threshold concentrations were lower in the MHS muscles. The correlations between myoplasmic [Ca²⁺] and force in MHS and normal muscles were similar.