Drug binding to rat skeletal muscle homogenate was studied using quinidine and quinine as basic drugs, and furosemide and phenylbutazone as anionic drugs. Characteristically different binding fashions were observed among basic and anionic drugs. Quinidine and quinine which are stereoisomers bound to muscle not depending on drug concenttation and showed similar binding ratios, while furosemide and phenylbutazone bound to muscle depending on drug concentration. Quinidine and quinine bound mainly to 1000×g precipitates of muscle homogenate while furosemide and phenylbutazone bound exclusively to cytosol fraction. Binding to 1000× g precipitates was not explained by binding to actin and myosin alone, while the second protein fraction eluted from cytosol by Sephadex G-75 gel filtration was found to have binding properties for furosemide.
