Effects of Variations in the Extracellular Osmolality on the Permeability to Nonelectrolytes of Vascular Smooth Muscle

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Abstract
Jonsson, O., Effects of variations in the extracellular osmolality on the permeability to non‐electrolytes of vascular smooth muscle. Acta physiol. scand. 1971. 81. 528–539.The effects of variations in the osmolality on the general permeability properties of the smooth muscle cell membranes have been studied by measuring the effluxes of 14C urea and 14C erythritol from rat portal veins at different extracellular tonicities. Permeability coefficients were calculated by introducing the rate constants for the cellular component of the washout curve as well as the estimated cell volume – cell surface ratios into a modified Fick's law of diffusion. The values obtained at normal tonicity of the washout medium were 8.78 10‐8 cm/sec for urea and 3.70 10‐8 cm/sec for erythritol. No definite alteration in the rate‐limiting properties of the cell membranes could be registered on exposure to hyperosmotic or moderately hypo‐osmotic (–54 mOsm/kg) media. However, when the tonicity of the washout medium was more markedly reduced (–109 mOsm/kg) a clearcut increase in the permeability coefficients for both substances was obtained. Possible explanations to this alteration in the permeability characteristics of the cell membranes on swelling of the smooth muscle cells are discussed.