[Influence of homologous n-alkanoic acids on functional properties of isolated skeletal muscles. I. Muscle contraction].

1. The contractility of isolated muscles of the frog (and in some instances of the rat) was investigated at room temperature in Ringer's solutions containing homologous alkanoic acids (100 mM C4 to 0.4 mM C10). 2. Free fatty acids decrease the contraction amplitudes evoked by direct stimulation. The effects increase with concentration, exposure, and chain length of the fatty acids. In Ringer's solution the changes are totally or partly reversible. 3. The depression of contraction amplitude induced by free fatty acids is removed by small concentrations of caffeine (2--5 mM) in Ringer's solution. 4. Interactions of fatty acids with different structures of skeletal muscle (mitochondria, sarcolemma and membranes of sarcoplasmic vesicles) are discussed. The distinct effect of fatty acids on stimulated muscles and the importance of membranes in the regulation of the calcium ion concentration in the cytoplasm suggest that fatty acids interact with membrane lipids.