EFFECTS OF MUCOSAL HYPEROSMOLARITY ON ACTIVE SUGAR TRANSPORT AND THE SUGAR-EVOKED POTENTIAL IN ISOLATED SMALL INTESTINE OF THE TOAD

Abstract

Isolated small intestines of toads were mounted in a flux chamber or suspended from a cannula as an everted sac, and osmolarity of solutions bathing the mucosal surface was changed by adding Dmannitol or polyethylene glycol to the standard solution. With increase in osmolarity we observed increases in (1) resistance of transmural water flow, (2) transmural electrical resistance, (3) tissue electrolyte content, (4) a decrease in water content of the tissue, (5) a change in transmural potential difference in the direction that the mucosal side becomes more positive, and (6) a reduction in size of the glucose-evoked potential. On the other hand the tissue uptake of D-glucose and Dgalactose from the mucosal solution did not significantly change with the treatment. Within a range of osmolarity change (less than 200 mOsm/liter), results (3) and (4) can be interpreted as due to a mere withdrawal of water from the tissue. The relationship between the size of the osmotic potential change and the osmolarity difference was similar to that between the rate of net water flow and the osmolarity difference. The fact that mucosal hyperosmolarity exerts strong influence on the sugarevoked potential but no significant influence on the uptake of sugar is interpreted as the effect of the hyperosmolarity being a consequence of changes in electrical resistance representing the lateral intercellular space.