Effect of age on activation of porcine intestinal guanylate cyclase and binding of Escherichia coli heat-stable enterotoxin (STa) to porcine intestinal cells and brush border membranes.
Development of age-dependent resistance to enterotoxigenic Escherichia coli was studied, using isolated enterocytes and brush border membranes (BBM) from 7-day-old and 7-week-old pigs. Binding of 125I-labeled heat-stable (125I-STa) enterotoxin to enterocytes and BBM was specific, temperature- and time-dependent, saturable, and partially reversible. Scatchard analysis revealed a single class of receptors. Mean +/- SD avidity of binding (apparent affinity constant, Ka) of 125I-STa to enterocytes from 7-day-old and 7-week-old pigs was 2.14 +/- 0.29 x 10(8) and 2.72 +/- 0.25 x 10(8) L/mol, respectively. Numbers of STa receptors were calculated to be 64,903 +/- 2,900/enterocyte for 7-day-old pigs and 53,029 +/- 3,117/enterocyte for 7-week-old pigs. Numbers of STa receptors expressed per milligram of BBM protein from 7-day-old pigs were 2.66 x 10(11), compared with 2.29 x 10(11) for BBM from 7-week-old pigs. By 5 minutes after addition of STa to reaction mixtures, intracellular cyclic guanosine monophosphate concentration increased 13.9-fold in enterocytes from 7-day-old pigs and 8.7-fold in enterocytes from 7-week-old pigs. The particulate guanylate cyclase activity associated with BBM from 7-week-old pigs was slightly more sensitive to low amounts of STa, compared with BBM from 7-day-old pigs; however, differences were not observed at intermediate and high amounts. These data indicate that lack of a secretory response to STa by older pigs is not attributable either to decreased numbers of STa receptors or to decreased signal response between the STa receptor and membrane-bound guanylate cyclase.(ABSTRACT TRUNCATED AT 250 WORDS)
Jaso-Friedmann
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Department of Microbiology, University of Kansas, Lawrence 66045.
Dreyfus
L A
LA
Whipp
S C
SC
Robertson
D C
DC
D000375:Aging / Q000276:immunology* / Q000378:metabolism; D000818:Animals; D001427:Bacterial Toxins / Q000378:metabolism*; D004768:Enterotoxins / Q000378:metabolism*; D004926:Escherichia coli / Q000276:immunology; D029968:Escherichia coli Proteins; D006162:Guanylate Cyclase / Q000378:metabolism*; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000382:microbiology*; D007457:Iodine Radioisotopes; D008871:Microvilli / Q000378:metabolism / Q000382:microbiology; D011956:Receptors, Cell Surface / Q000378:metabolism*; D000074261:Receptors, Enterotoxin; D050705:Receptors, Guanylate Cyclase-Coupled; D018000:Receptors, Peptide; D013552:Swine / Q000276:immunology / Q000378:metabolism / Q000382:microbiology*; D013696:Temperature
D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D007457:Iodine Radioisotopes; D011956:Receptors, Cell Surface; D018000:Receptors, Peptide; C034151:heat stable toxin (E coli); D006162:Guanylate Cyclase; D000074261:Receptors, Enterotoxin; D050705:Receptors, Guanylate Cyclase-Coupled