Presence of functional receptors for the Escherichia coli heat-stable enterotoxin in the gastrointestinal tract of the chicken.

Receptors for the Escherichia coli heat-stable enterotoxin (STa) were shown to be present throughout the digestive tract of the chicken, with binding activity present not only in the intestinal epithelium but also in the intestinal smooth muscle. Brush border membrane vesicles (BBMV) purified from chicken enterocyte homogenates and plasma membranes (SMPM) purified from intestinal smooth muscle homogenates were compared with pig enterocyte BBMV. All had similar 125I-STa binding affinities, but the 50% effective concentration for STa activation of guanylate cyclase was higher in SMPM than in BBMV. Maximal STa-stimulated guanylate cyclase activities were similar in chicken and pig BBMV and were seven- to eightfold higher than in SMPM, and the STa receptor density was five- to sixfold higher. Patterns unique to each membrane were demonstrated after affinity labelling of STa receptors with 125I-STa, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and autoradiography. The results demonstrated STa-stimulated guanylate cyclase activity in birds as well as mammals and suggested that there are different functional STa receptors in chicken BBMV and SMPM.