A correlation had previously been established between actomyosin content of homogenized skeletal muscle cell segments as determined by extraction in strong salt solution and the ability of those segments to empty when extracted with buffered water. In this study, we examined the ability of certain compounds to inhibit the process of emptying. Adenosine triphosphate (ATP) and adenosine diphosphate (ADP), which dissociate actomyosin, inhibited the process of emptying, while adenosine monophosphate (AMP) which does not dissociate actomyosin, did not. We conclude that the formation of actomyosin is a necessary prerequisite for emptying and not just a secondary effect. Polyvalent cations were also found to inhibit emptying. The inhibition was reversible by washing with a solution of NaCl-histidine or with chelating agents, ethylenediaminetetraacetate (EDTA) and ethylene-glycol-bis(ß-amino-ethyl ether) tetraacetic acid (EGTA). A factor(s) solubilized from aged muscle functions as an inhibitory agent; the suggestion is made that this factor(s) may be a polyvalent cation.

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