| Abstract: | Calcium efflux from skeletal muscle fragmented sarcoplasmic reticulum was studied using a dilution technique and Millipore filtration. In the absence of Mg++ and external Ca++, addition of lmM adenosine triphosphate to the suspension resulted in an immediate loss of 26–55% of total vesicular calcium. The amount of calcium released was calculated to be sufficient to effect muscle contraction. After separation of the sarcoplasmic reticulum into light, intermediate and heavy vesicles, the light and heavy fractions were found to be only weakly responsive to adenosine triphosphate, whereas the intermediate fraction lost nearly half of its calcium. The significance of these results with respect to excitation-contraction coupling in muscle is discussed. |
