Estimation of Extracellular Spaces of Smooth Muscle Using Different-sized Molecules.

BARR, LLOYD, AND RICHARD L. MALVIN. Estimation ofextracellular spaces of smooth muscle using di$erent-sized molecules. Am. J. Physiol. 208(5) : IO@-1045. Ig65.-The apparent fraction of tissue water available as solvent was determined for a number of test substances: urea, arabinose, mannitol, sucrose, raffinose, inulin, and radioiodinated serum albumin. The apparent extracellular spaces decrease with increasing molecular size. Urea seems to come to concentration equilibrium in all tissue water. Arabinose and mannitol values are close together at about 70% tissue water. Similarly sucrose, raffinose, and inulin values cluster at about 48y0 tissue water, while RISA can reach only about 20%. The amounts of sodium, potassium, and chloride in canine intestinal smooth muscle are similar to values given for other smooth muscle. Intracellular ion concentrations similar to those of other tissues can be calculated if the true extracellular space is between that measured by RISA and sucrose.