Effect of quercetin on tension development by skinned fibres from frog skeletal muscle

For proper interpretation of the results of drug-induced calcium release experiments with skinned fibres, it is necessary to know the direct effects of the drug on the contractile system. We examined the action of quercetin and its various solvents on mechanically skinned skeletal muscle fibre which is deprived of functioning sarcoplasmic reticulum by Triton X-100. Dimethyl sulphoxide (DMSO) at 1%, a solvent for quercetin, decreased reversibly Ca2+ sensitivity for the contractile system of frog skeletal muscle. Alcohol was similar to dimethyl sulphoxide. Polyethylene glycol was used as a solvent for quercetin, because the solvent at 1% was found to be inert to the pCa-tension relationship. Quercetin increased reversibly Ca2+ sensitivity of the contractile system with the unchanged maximum tension, the pCa-tension relationship being less steep. Since quercetin did not change calcium binding to troponin C from rabbit skeletal muscle, the effect may be due to modified molecular interactions which follow calcium binding to troponin C. The drug might also affect the interaction between troponin subunits. Because DMSO did not affect calcium binding to troponin C, either DMSO also modulates the interaction between troponin subunits and/or it modulates molecular interactions after calcium binding which lead to tension development.