Effect of caffeine and glycerin on the Ca transport system of sarcoplasmic reticulum fragments from frog skeletal muscles

Parameters of the Ca2+-ion transport system by a fragmented sarcoplasmic reticulum isolated from phasic and tonic frog skeletal muscles were investigated under the action of caffeine or caffeine in combination with glycerol. No changes were observed in the Ca-transport system of a light fraction of the sarcoplasmic reticulum under the influence of caffeine and caffeine-glycerol combination. Caffeine reduced the value of Ca/ATP and enhanced the outflux of Ca2+-ions from membrane fragments of the caffeine-sensitive sarcoplasmic reticulum fraction of both the muscles; the combined effect of caffeine and glycerol was analogous to the action of caffeine applied alone. It is concluded that the potentiation of muscle contraction in the presence of glycerol is not due to the excess of Ca-release from the sarcoplasmic reticulum caused by this agent.