Distribution of nonelectrolytes in muscle

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Abstract
Uptake and rate of efflux of some nonelectrolytes was studied in stomach muscle and sartorius of the frog. After complete equilibration the concentration in muscle water approximated that of the medium for glycerol, but was higher for urea and thiourea. Erythritol space averaged 50%. d-Arabinose and sucrose distributed themselves in a smaller volume, which, however, was always greater than that of inulin. Efflux of sugars did not follow first-order kinetics and became very slow after a few hours. This was true also for muscles washed in formalin. In glycerol-extracted muscle fibers, sucrose space was nearly as large as water space, but inulin space was significantly lower. It is concluded that sugars and some other nonelectrolytes penetrate into the fibers but are excluded from part of the intracellular water and, therefore, produce osmotic effects. The results support the hypothesis that most of the fiber water is contained in segregated or narrow spaces, hindering diffusion of all except very small molecules.