Osmotic effects and diffusion of nonelectrolytes in muscle

¹ Department of Physiology, Ohio State University, Columbus, Ohio

Osmotic effects and distribution of some nonelectrolytes were studied in the frog's sartorius and stomach muscle. Diffusion of urea and thiourea, determined by chemical methods, was more than 90% complete in 1 hour. Nevertheless Ringer's solution to which these substances were added caused reversible shrinkage which, in the sartorius, persisted for many hours. To explain this result and previous observations on stomach muscle it is suggested that a large part of the fiber water is contained in narrow spaces, hindering diffusion of molecules as small as those of urea. That semipermeability is a property of muscle fibers in bulk is supported by the observation that sugars have a long lasting osmotic action on thin transverse slices of the sartorius. This hypothesis also explains that, at the same osmotic pressure, the osmotic effects of nonelectrolytes vary widely, increasing in the order urea < erythritol < ribose < sucrose.