Calcium waves induced by hypertonic solutions in intact frog skeletal muscle fibres

1. Regenerative Ca2+ waves and oscillations indicative of calcium-induced c alcium release (CICR) activity were induced in fully polarized, fluo-3-load ed, intact frog skeletal muscle fibres by exposure to hypertonic Ringer sol utions. 2. The calcium waves persisted in fibres exposed to EGTA-containing solutio ns, during sustained depolarization of the membrane potential or following treatment with the dihydropyridine receptor (DHPR)-blocker nifedipine. 3. The waves were blocked by the ryanodine receptor (RyR)-specific agents r yanodine and tetracaine, and potentiated by caffeine. 4. In addition to these pharmacological properties, the amplitudes, frequen cy and velocity of such hypertonicity-induced waves closely resembled those of Ca2+ waves previously described in dyspedic skeletal myocytes expressin g the cardiac RyR-2. 5. Quantitative transmission and freeze-fracture electronmicroscopy demonst rated a reversible cell shrinkage, transverse (T)-tubular luminal swelling and decreased T-sarcoplasmic reticular (SR) junctional gaps in fibres maint ained in and then fixed using hypertonic solutions. 6. The findings are consistent with a hypothesis in which RyR-Ca2+ release channels can be partially liberated from their normal control by T-tubular DHPR-voltage sensors in hypertonic solutions, thereby permitting CICR to op erate even in such fully polarized skeletal muscle fibres.