A POSSIBLE ROLE OF SARCOPLASMIC CA2-MUSCLE( RELEASE IN MODULATING THESLOW CA2+ CURRENT OF SKELETAL)

Ca2+ channels are regulated in a variety of different ways, one of whi ch is modulation by the Ca2+ ion itself. In skeletal muscle, Ca2+ rele ase sites are presumably located in the vicinity of the dihydropyridin e-sensitive Ca2+ channel. In this study, we have tried to investigate the effects of Ca2+ release from the sarcoplasmic reticulum on the L-t ype Ca2+ channel in frog skeletal muscle, using the double Vaseline ga p technique. We found an increase in Ca2+ current amplitude on applica tion of caffeine, a well-known potentiator of Ca2+ release. Addition o f the fast Ca2+ buffer BAPTA to the intracellular solution led to a gr adual decline in Ca2+ current amplitude and eventually caused complete inhibition. Similar observations were made when the muscle fibre was perfused internally with the Ca2+ release channel blocker ruthenium re d. The time course of Ca2+ current decline followed closely the increa se in ruthenium red concentration. This suggests that Ca2+ release fro m the sarcoplasmic reticulum is involved in the regulation of L-type C a2+ channels in frog skeletal muscle.