DEVELOPMENTAL DIFFERENCES IN THE EXPRESSION OF THE CHOLERA-TOXIN SENSITIVE SUBUNIT (GS-ALPHA) OF ADENYLATE-CYCLASE IN THE RAT SMALL-INTESTINE

Background-The stimulatory guanosine triphosphate (GTP) binding protei n alpha subunit (Gs alpha) of adenylate cyclase is the target protein for cholera toxin. Aims/methods-The expression of this signal transduc er was analysed in the small intestine of developing rats by RNA trans fer (northern blot) analysis by immunoblotting, and by ADP-ribosylatio n of membrane proteins. Results-Intestinal Gs alpha mRNA (about 1 . 9 kb) was increased in the neonate compared with the adult rat. Two isof orms of Gs alpha proteins, a 45 000 and a 52 000 form, were expressed in the small intestinal epithelial cell and both were ADP-ribosylated by cholera toxin. A significant increase in the larger isoform (52 000 ) and in its ribosylation was noted in the 2 week old suckling compare d with post-weaned older animals. The protein content or ribosylation of the smaller form (45 000) did not significantly change with age. Co nclusion-These data show that a developmental decline of intestinal Gs alpha expression seems to be, in part, regulated at the mRNA level. A n increased Gs alpha expression in the immature intestine may help to explain a previously reported, dose dependent increased adenylate cycl ase response and an increase in fluid secretion to cholera toxin in ne onates compared with adults.