Stimulation by anoxia of active chloride transfer in isolated bullfrog small intestine

Abstract

1. 1. In isolated bullfrog small intestine mounted between identical isotonic Na 2SO 4 Ringer solutions at pH 7.2, potential difference (PD) and short circuit current ( I sc ) are largely inhibited by N 2 and by 2,4-dinitrophenol. The residual PD and I se sometimes found in the presence of N 2 is abolished by mucosal fluoride. Following moderately short exposures, the inhibitory effects of N 2 are completely reversed by O 2. Following prolonged exposure to N 2, PD and I sc are only partially restored by O 2. 2. 2. When the tissue is mounted between identical Ringer solutions in which Na + is completely replaced by Tris ions, PD (serosal negative) and I sc are markedly increased under anoxic conditions. In the presence of metabolized sugar (glucose or fructose) these increases are sustained and are reversed by O 2. Glucose is effective whether it is present initially in the mucosal medium, the serosal medium, or both. The increase in PD and I sc observed with mucosal glucose is not inhibited by phlorizin. In substrate-free media or in media containing non-metabolized or poorly metabolized solutes ( 3-O- methylglucose , sorbose or valine) N 2 elicits a transient increase only in PD and I se . In the presence of glucose, 2,4-dinitrophenol (mucosal or serosal) elicits increases in PD and I se similar to those induced by N 2. In media containing glucose, N 2 markedly increases m → s Cl − flux but does not change s → m Cl − flux. The increased m → s Cl − flux under these conditions is significantly greater than the corresponding increase in I se . Part of the discrepancy between these parameters can be attributed to a net co-transport of K + from the mucosal to the serosal medium.