Ontogenesis of ?2-Adrenoceptor Coupling with GTP-Binding Proteins in the Rat Telencephalon

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Abstract
The ontogenesis of .alpha.2-adrenoceptors and GTP-binding proteins and their coupling activity were investigated in telecephalon membranes of developing rats. The manganese-induced elevation of [3H]clonidine binding was increased in an age-dependent manner but the guanosine 5''-O-(3-thio)triphosphate-induced decrease in binding did not change. The extent of the binding of [3H]clonidine at 15 nM (saturable concentration) increased in an age-dependent manner and reached the adult level at 4 days after birth. Cholera toxin and pertussis toxin catalyzed ADP-ribosylation of proteins of 46 and 41/39 kilodaltons (kDa) in solubilized cholate extracts of the membranes. The 41/39-kDa proteins ADP-ribosylated by pertussis toxin (Gi.alpha. + Go.alpha.) were increased with age and reached the adult level at day 12, whereas the 46-kDa protein (Gs.alpha.) reached its peak on day 12 and then decreased to the fetal level at the adult stage. The immunoblot experiments of the homogenates with antiserum (specific antibody against .alpha.- and .beta.-subunit of GTP-binding proteins) demonstrated that the 39-kDa .alpha.-subunit of (Go.alpha.) and the 36-kDa .beta.-subunit of GTP-binding protein (.beta.36) increased with postnatal age. In contrast, 35-kDa .beta.-subunit (.beta.35) did not change. From these results, it is suggested that the coupling activity of .alpha.2-adrenoceptor with GTP-binding protein gradually develops in a manner parallel with the increase of .alpha.2 adrenoceptor and pertussis toxin sensitive GTP-binding proteins, Gi, and that .alpha.39.beta.36.gamma. may be related to the differentiation and/or growth of nerve cells in rat telencephalon.