MEASUREMENT OF CALCIUM-RELEASE FROM THE SARCOPLASMIC-RETICULUM INTO THE MYOPLASM OF FROG CUT MUSCLE-FIBERS

Ca release from the sarcoplasmic reticulum of frog cut muscle fibers h as been estimated with two different methods. The first method is to m easure the myoplasmic free [Ca] transient under nonperturbing conditio ns and then estimate the amounts of Ca that are bound to the myoplasmi c buffers troponin and parvalbumin. The Ca released from the sarcoplas mic reticulum is estimated from the sum of the concentrations of free Ca and of Ca bound to the indicator, to troponin, and to parvalbumin. The second method is to estimate the amount of Ca release by capturing most of the Ca with a large concentration of a high affinity Ca buffe r. Both methods give similar estimates of the amount of Ca release fol lowing a single action potential and of the shape and amplitude of the release waveform.