Effects of glucose and ouabain on transepithelial electrical resistance and cell volume in stripped and unstripped goldfish intestine

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Abstract
In goldfish intestine (perfused unstripped segments and mucosal strips) the serosal addition of ouabain (10\t-4 M) resulted in a vanishment of the transepithelial potential difference and in a continuous increase in transepithelial resistance. Incubation of mucosal strips with ouabain resulted in an increase in sodium content which was greater than the decrease in potassium content. The resulting increase in cation content was accompanied by an increase in chloride content and an increase in water content. Histological examination showed that exposure to ouabain resulted in a swelling of the epithelial layer as compared to the control situation. The ouabain induced resistance increase is greater in the presence of glucose, 3-OMG or fructose than in the presence of mannitol. Phlorizin (10\t-4 M) inhibits the extra resistance increase induced by mucosal glucose but is without effect on the fructose induced extra resistance increase. The initial velocity and the magnitude of the glucose induced extra resistance increase depends on the glucose concentration. The results suggest that in goldfish intestine ouabain induces cellular swelling with a concomitant collapse of the lateral intercellular spaces, which is the cause of the increased transepithelial resistance. The additional changes in resistance induced by sugars suggest that the cell membrane is more permeable to glucose, 3-OMG and fructose than to mannitol. The resulting changes in osmotically active material within the epithelial cell influence the cross-sectional area and consequently the conductivity of the paracellular shunt pathway. The hypothesis that these sugars do not induce a resistance change in the absence of ouabain is discussed.