Inhibition of D-galactose and L-phenylalanine transport by HgCl2 in rat intestine in vitro

Abstract

The effect of Hg2+ on galactose and phenylalanine uptake has been studied in rat everted intestinal rings incubated for 2 minutes. The presence of 0.5 mM Hg2+ in the incubation medium inhibited the total galactose uptake from 30% to 40% and that of the phenylalanine about 70%. The inhibition was due to a reduction of galactose transport and Na(+)-dependent phenylalanine transport. Hg2+ inhibited the galactose transport in a non-competitive way, with a Vmax diminution without Km modification. The Na(+)-dependent phenylalanine transport was totally blocked in the presence of 1 mM Hg2+. The washing of the intestinal rings with 5 mM EDTA slightly decreased the inhibition produced by 0.5 mM Hg2+ on phenylalanine uptake whereas it did not modify the inhibition of galactose uptake. However, the inhibition of galactose uptake was completely reversed after washing with 10 mM cysteine. Therefore, phenylalanine transport seems to be more sensitive to HgCl2 than galactose transport. The inhibition of these intestinal transport systems by Hg2+ might be due to its interaction with ligands of the transport proteins located in the luminal membrane of enterocytes.