EFFECTS OF RYANODINE ON PERMEABILITY OF CHOLINE AND GLUCOSE THROUGH CALCIUM CHANNELS IN SARCOPLASMIC-RETICULUM VESICLES

The effect of ryanodine on the permeation of glucose, choline, and Ca2+ through the Ca2+ channel in sarcoplasmic reticulum vesicles was studied by means of the light scattering and/or the tracer method. Ryanodine had the same effect on the permeabilities of choline and Ca2+; low concentrations of ryanodine (10 muM) locked the channel in the open state, and high concentrations (100 muM) opened the channel transiently, which closed finally. Glucose became permeable on the ryanodine treatment even in the absence of KCl, although it was not permeable before the treatment when the channel was open. Submolar concentrations of KCl enhanced the glucose and choline permeability of the ryanodine-treated channel as well as the untreated one. Activators such as ATP and caffeine did not enhance the permeability of the treated channel in the open locked state, but-inhibitors such as Mg2+ and ruthenium red closed the channel, although much higher concentrations were required than for the untreated channel. The maximal rates of choline and glucose permeation of the ryanodine-treated channel were lower than those of the untreated one attained in the presence of ATP and/or caffeine. This result is consistent with the fact that the single channel conductance after the ryanodine treatment decreased to 40-50% of the maximal conductance of the untreated one. This result suggests that the conformation of the channel opened by ryanodine was different from that with ATP or caffeine.