Permeability of Smooth Muscle

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Abstract
Penetration of sucrose into the muscle fibers of the frog's stomach is inferred from the observation that muscles swell in isosmotic sucrose solution and that sucrose space is consistently, on the average by 34%, larger than inulin space. In solutions of low electrolyte concentration water uptake and loss are strongly influenced by the presence of small amounts of Ca++ or Mg++. Thus muscles swell in isosmotic sugar solutions, but shrink after the addition of 2 mm CaCl2 or MgCl2. Also, swelling is several times smaller in 2 mm CaCl2 or MgCl2 than in pure water in spite of a smaller loss of electrolytes from the fibers. Swelling in sugar solutions and in diluted Ringer's solution is associated with a considerable loss of electrolytes from the fibers, which probably is partly responsible for the swelling. It is concluded that the charge of protein and intermolecular forces are important factors determining fiber volume. Although sucrose and fructose rapidly penetrate into the fibers, the spaces they occupy are much smaller than that of water. Most of the fiber volume, therefore, is not available as solvent for the sugars and may be ‘bound.’

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