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Water transport revisited

D. W. Powell

Nearly forty years ago Curran & MacIntosh (1962) presented experimental evidence for a model of water transport that would satisfy a question posed by such famous physiologists as Heidenhain and Reed before the turn of the century: how can the intestine accomplish transport of water from one isotonic compartment (the bowel lumen) to another (the blood)? Curran, who was a superb experimentalist as well as a theoretician, had previously shown that water transport bore a linear relationship to solute (Na⁺) transport. He and MacIntosh then demonstrated that a three-compartment model (see Fig. 1) would allow movement of fluid from compartment I to III as long as compartment II contained a solution hypertonic to I and III, and as long as the permeabilities (reflection coefficients) of the membranes A and B, which separated the compartments, were finite with B greater than A. They used cellophane for membrane A and sintered glass for membrane B in their model. The biological counterparts to these membranes were thought to be the tight junctions (TJ) of the epithelial cells for membrane A, the basement membrane (BM) for membrane B and the intercellular space (ICS) for compartment II. Active Na⁺ transport along the basolateral membrane of the epithelial cell into the ICS was proposed as the active solute's transport step driving the passive flow of water from I to III. Diamond's 'standing gradient' hypothesis of water movement was a later variation of this model (Diamond, 1978). Thus, the mystery of the special driving force, or 'treibkraft' moving water across the intestinal wall was solved: it was 'compartmentalized' osmotic pressure.

This article has been cited by other articles:

				D. W. Powell, R. C. Mifflin, J. D. Valentich, S. E. Crowe, J. I. Saada, and A. B. West Myofibroblasts. II. Intestinal subepithelial myofibroblasts Am J Physiol Cell Physiol, August 1, 1999; 277(2): C183 - C201. [Abstract] [Full Text] [PDF]