Rheogenic property of Na+/acidic amino acid co-transport by guinea pig intestine.

Abstract

The influx of L-glutamate or L-aspartate across the intestinal brush border membrane was absolutely dependent on the presence of Na+ in the mucosal solution and saturable. The addition of these amino acids into the mucosal solution induced a sudden and sustained increase in the transepithelial potential difference (PDt), which was found to be absolutely dependent on the presence of Na+ in the mucosal solution. The increases in PDt induced by L-glutamate or L-aspartate conformed to Michaelis-Menten kinetics against the concentration of each organic substrate. On the other hand, the relationship between the change in short-circuit current induced by acidic amino acid and Na+ concentration did not conform to Michaelis-Menten kinetics but was sigmoid. A kinetic study indicated that 2 Na+ were translocated per molecule of the acidic amino acid. The PDt was not altered by the total replacement of K+ by Na+ in the mucosal solution and showed the optimum pH at around 7. The transfer of L-glutamate from mucosal to serosal solution was examined with everted sac of ileum. A significant increase in serosal appearance was observed for L-glutamate and L-alanine after the incubation with L-glutamate. The serosal appearance of L-glutamate was unaffected by the presence or absence of HCO3-.