Abstract

Hypertonic solutions cause a slow, transient increase in ⁴⁵Ca efflux of 40 minutes duration, a net loss of total muscle calcium and a 90% decrease in caffeine contracture tension. Electrical stimulation of muscles in hypertonic solution does not lead to an increase in ⁴⁵Ca efflux, whereas caffeine still causes an increase in ⁴⁵Ca efflux. "Glycerol-treated" muscles undergo an 8-fold increase in ⁴⁵Ca influx during the first 60 minutes of recovery with no corresponding increase in efflux, resulting in a net gain of 0.68 µmol/g wet weight of calcium: the increases in ⁴⁵Ca influx and efflux during K⁺ depolarization do not appear to be altered by glycerol treatment. The magnesium content of glycerol-treated muscles is decreased by 4.06 µmol/g and potassium content by 42.3 µmol/g; this is associated with an increased efflux of Mg⁺⁺. When glycerol treatment takes place in the presence of 5 mM Ca⁺⁺ and 5 mM Mg⁺⁺, the magnesium content is increased to 10.63 µmol/g and the potassium is increased to 80.0 µmol/g. In glycerol-treated muscle the sarcolemmal membrane appears to govern influx, but the sarcoplasmic reticulum restricts efflux of calcium from the muscle by sequestration of calcium into an intracellular compartment and maintaining the myoplasmic free calcium below 10^-7 M, i.e., consistent with the relaxed state of the muscle.