Sugar-induced potential difference and short circuit current in bullfrog small intestine: effect of UO22+

UO22+ 1.3 mM added as UO2(NO3)2 to the mucosal solution consistently inhibited the P.D. and ISC 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 SO42- was the major anion. The average degree of inhibition in the presence of glucose was 42 +/- 7(SEM) percent. P.D. and ISC in the absence of transported solutes were not significatnly altered by mucosal UO22+ at this concentration. Increasing the mucosal UO22+ concentration to 2.6 mM did not significantly increase its inhibitory action on glucose-evoked P.D. and ISC. Further increasing the UO22+ concentration to 13 mM completely inhibited glucose-induced P.D. and ISC but also markedly reduced these parameters in the absence of glucose. Serosal UO22+ (1.3mM) had no effect on the P.D. and ISC evoked by glucose and 3-O-methyl glucose. It is suggested that the inhibitory action of UO22+ involves binding of this ion to anionic sites located in the apical membrane of the absorptive cells. Mucosal or serosal UO22+ (1.3 mM) had no effect on the P.D. and ISC elicited by 20 mM valine, indicating that under the conditions of these experiments UO22+ selectively inhibits sugar-induced P.D. and ISC and, by implication mucosal sugar uptake.