Mercury inhibits the transport of d-glucose by the intestinal brush border membrane vesicles of fish

Abstract

Mercury compounds (HgCl 2 and CH 3HgCl) in polluted coastal waters accumulate in the food chain. When the food is digested in the gut of invertebrates and fish Hg 2+ and CH 3Hg + bind to the brush border membrane of the enterocytes facing the lumen of the intestine. It has been shown that under in vivo or in vitro tissue incubation the bound mercury inhibits the absorption of nutrients such as amino acids and sugars. In order to differentiate the membrane effect from intracellular metabolic effects brush border membrane vesicles were prepared and purified. These vesicles showed 6–7-fold enrichment for alkaline phosphatase, leucine aminopeptidase, and maltase—all membrane enzymes that face the lumen. There was little or no enrichment for Na +K + ATPase considered to be on the basolateral membranes of the enterocyte. The vesicles transported glucose when provided with a Na + electrochemical gradient. This transport was abolished in the absence of Na + electrochemical gradient or in the presence of Phlorizin. At 0·1mM glucose, HgCl 2 (20 ppm) abolished 90% of this transport and CH 3HgCl (20 ppm) abolished 30% of the transport. At 1mM glucose the inhibition values were 70% and 32% respectively. In the case of HgCl 2 inhibition of transport is significant even at 5 ppm. These findings confirm that mercury compounds can interact with intestinal brush border membranes to inhibit nutrient absorption in fish feeding in polluted waters.