Sugar-Induced Potential Difference and Short Circuit Current in Bullfrog Small Intestine: Effect of UO 2 2+

Summary

UO₂ ²⁺ 1.3 mM added as UO₂(NO₃)₂ to the mucosal solution consistently inhibited the P.D. and I _sc evoked by 11 mM glucose and 35 mM 3-O-methyl glucose across isolated strips of bullfrog small intestine bathed by symmetrical Ringer solutions in which SO₄ ^2- was the major anion. The average degree of inhibition in the presence of glucose was 42 ± 7 (SEM) percent. P.D. and I _sc in the absence of transported solutes were not significantly altered by mucosal UO₂ ²⁺ at this concentration. Increasing the mucosal UO₂ ²⁺ concentration to 2.6 mM did not significantly increase its inhibitory action on glucose-evoked P.D. and I _sc. Further increasing the UO₂ ²⁺ concentration to 13 mM completely inhibited glucose-induced P.D. and I _sc but also markedly reduced these parameters in the absence of glucose. Serosal UO₂ ²⁺ (1.3 mM) had no effect on the P.D. and I _sc evoked by glucose and 3-O-methyl glucose. It is suggested that the inhibitory action of UO₂ ²⁺ involves binding of this ion to anionic sites located in the apical membrane of the absorptive cells. Mucosal or serosal UO₂ ²⁺ (1.3 mM) had no effect on the P.D. and I _SC elicited by 20 mM valine, indicating that under the conditions of these experiments UO₂ ²⁺ selectively inhibits sugar-induced P.D. and I _SC and, by implication, mucosal sugar uptake.