Escherichia coli heat stable enterotoxin receptors & guanylyl cyclase activity in the intestinal brush border membrane of hamsters & guinea pigs.
OBJECTIVE
Although Escherichia coli heat stable enterotoxin (STa) causes diarrhoea in laboratory animals, no studies were done to find out the species specific variation of distribution of the STa receptors in laboratory animals. The present investigation evaluates the density of STa receptors and the guanylyl cyclase (GC) activity in the small intestinal epithelial cells of hamsters and guinea pigs.


METHODS
Brush border membrane (BBM) was prepared from the small intestines of hamsters and guinea pigs. Receptor binding assay, GC assay and autoradiography were performed to determine the density of STa receptors, the GC activity and molecular weights of the STa binding proteins respectively.


RESULTS
The receptor densities, per mg BBM protein at equilibrium, were found to be 4.1 x 10(9) and 1.5 x 10(12) in hamsters and guinea pigs respectively. The GC activity was found to be lower in STa treated hamster BBM compared to that of guinea pig. Scatchard analysis of the stoichiometric data showed a linear plot, and STa bound with association constants of 0.31 x 10(12) M-1 and 1.04 x 10(12) M-1 in hamsters and guinea pigs respectively. Autoradiographic analysis of the SDS-PAGE, revealed that 125I-STa bound apparently to a 45 kDa membrane protein in hamster and a 115 kDa membrane protein in guinea pig.


CONCLUSIONS
It appears that a lower density of STa receptor exists in hamsters compared to that in guinea pigs. STa binds with a single population of STa receptors in each species with different ligand binding affinities. Also, the molecular weights of the STa binding proteins differ in these species. Moreover, the GC activity was found to be lower in hamsters than in guinea pigs.
Division of Pathophysiology, National Institute of Cholera & Enteric Diseases, Calcutta, India.
J
J
Bhattacharya
S
S
Samanta
K M
KM
Hoque
A
A
Mukherjee
M K
MK
Chakrabarti
D000818:Animals; D006224:Cricetinae; D004355:Drug Stability; D004926:Escherichia coli / Q000378:metabolism*; D006162:Guanylate Cyclase / Q000737:chemistry / Q000378:metabolism*; D006168:Guinea Pigs; D006358:Hot Temperature; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000382:microbiology*; D008647:Mesocricetus; D008871:Microvilli / Q000378:metabolism / Q000382:microbiology; D000074261:Receptors, Enterotoxin; D050705:Receptors, Guanylate Cyclase-Coupled; D018000:Receptors, Peptide / Q000737:chemistry / Q000378:metabolism*
D018000:Receptors, Peptide; D006162:Guanylate Cyclase; D000074261:Receptors, Enterotoxin; D050705:Receptors, Guanylate Cyclase-Coupled