Binding of Escherichia coli heat-stable toxin and rise of guanylyl cyclase activity in the brush-border membranes of rabbit intestinal epithelial cells

The study examines the age-related differences in the density of Escherichia coli heat-stable enterotoxin (STa) receptors in the small intestine of rabbits. The number of STa receptors was found to be 1.7 x 10(12) in 14-day old rabbits compared to 2.4 x 10(9) in 14-week old rabbits per milligram brush-border membrane protein. The STa-induced guanylyl cyclase activity in the intestinal brush-border membranes was found to be stimulated by 6.2 folds over the basal enzyme activity in 14-day old rabbits, whereas in the 14-week old rabbits, it was 4 folds over the basal activity. Moreover, the enzyme activity remained lower in the adult rabbits compared to the younger ones. Autoradiographic analysis of sodium dodecyl sulphate polyacrylamide gel electrophoresis showed two STa-binding proteins of apparent molecular weights of 140 and 38 kDa in the intestinal brush-border membranes of rabbits.