Sugar-dependent Increment of the Transmural Potential of Isolated Small Intestine in Li<sup>+</sup>-medium

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  • Sugar-dependent increment of the transmural potential of isolated small intestine in Li+-medium

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The generation of the sugar-dependent increment of the transmural potential (the sugar-evoked potential) was studied in Li+-medium using everted sacs of toad intestine. A distinct immediate increment of the potential difference (PD) was observed in Li+-medium when actively transported sugar was added to the mucosal solution, though its maximum amplitude was smaller as compared with that in Na+-medium. The relative magnitude (ΔPD in Li+-medium versuso ΔPD in Na+-medium) was dependent on sugar concentration and seasons. Distinct characteristics of the evoked potential generated in Li+-medium were its relatively rapid spontaneous decay (failure of plateau formation) and independence of its configuration of oxygen supply. Li+ had a small stimulating effect on the tissue uptake of glucose, which was abolished by an addition of 2×10-4M phlorizin. Tissue to medium concentration ratio for glucose never exceeded unity in Li+-medium. The results can be interpreted as indicating that Li+ can interact with sugar carriers at the mucosal border and stimulate them but it is not extruded actively out of the mucosal cells, and that the genesis of the sugar-evoked potential is associated with a movement of sugar-Li+-carrier complexes within the mucosal border of the epithelial cells.

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