Ryanodine and theophylline-induced depletion of energy stores in amphibian muscle

Abstract

The effects of high and low levels of ryanodine on theophylline-induced energy depletion were studied in isolated frog sartorius muscle. Whereas low concentrations of ryanodine (1–10 μM) did not change high energy phosphate contents (PE) after 60 min, high levels (100 μM) reduced resting energy contents by 60% after 60 min. Subcontracture levels of theophylline (2 mM), in the presence of high ryanodine, produced an 80% PE depletion, suggesting possible additive or synergistic effects of these two agents. In contrast to theophylline-induced depletion, neither the ryanodine-induced depletion nor the theophylline-plus-ryanodine-induced depletion of PE seemed sensitive to inhibition by 1 mM procaine. This suggests that there may be differences in the mechanisms whereby methylxanthines and ryanodine deplete energy stores and evoke contractures in amphibian skeletal muscle.