Age-dependent variation in the density and affinity of Escherichia coli heat-stable enterotoxin receptors in mice

Enterotoxigenic strains of Escherichia coli that produce heat-stable entero toxin (STa). are a major cause of diarrheal disease worldwide. Resistance t o diarrheal disease in human infants and newborn animals has been attribute d to a gradual turnover in the intestinal brush border membrane receptors t o bacterial pill. In this study, we demonstrated age-dependent variation in the density and affinity of the mouse enterocyte receptors specific for ST a. Flow cytometry and radiolabeled-STa (I-125-STa) assays were used as more reliable quantitative measures for the characterization of STa-enterocyte receptor interaction. These assays indicated a stronger interaction of STa with its putative receptor on the enterocytes of the 2-day-old suckling mic e than with enterocytes from 1-week, 2-week and 2-month-old mice. Scatchard plot analysis of I-125-STa-receptor interaction suggested that STa-recepto rs exist at a higher number on enterocytes from the 2-day-old mice than ent erocytes of the older mice. Additionally, receptors from the 2-day-old mice had a greater affinity for STa ligand than receptors from the older mice. Density of STa receptors on enterocytes and their affinity to STa may deter mine the extent of binding and severity of secretory response. This may fur ther explain the increased susceptibility of newborn animals and human infa nts to STa-mediated diarrheal disease.