Striatal [3H]GTP binding in developing rats: involvement of sulfhydryl residues, Ca2+ and Mg2+

Effects of adenosine on cAMP production during early development in the optic tectum of chicks

Accumulation of cyclic adenosine monophosphate (cAMP) elicited by adenosine was studied in slices and membrane preparations of optic tectum from chicks aged 1-13 days post-hatch. Accumulation of cAMP promoted by adenosine declined with age, the highest value being observed in three-day-old chicks and the lowest in 11-day-old chicks. However, when the slices were incubated with adenosine and the phosphodiesterase inhibitor-Ro 20-1724 the differences between the two ages were abolished, suggesting a higher phosphodiesterase activity in 11-day-old chicks. In membrane preparations, although basal adenylate cyclase activity was lower in three-day-old chicks, the guanylyl-imidodiphosphate (Gpp(NH)p) concentration curves for stimulation of adenylate cyclase activity indicated a higher sensitivity of G protein to Gpp(NH)p at this age. This hypothesis was reinforced by the observation that the binding of [3H]Gpp(NH)p to the membrane preparation was greater in three-day-old animals. In spite of these differences, the percentage of adenylate cyclase activity stimulation by 2-chloroadenosine (2CADO)+Gpp(NH)p was the same at both ages. These findings suggest that the decreased response evoked by adenosine during development is probably due to increased phosphodiesterase activity and a lower sensitivity of adenylate cyclase activity to Gpp(NH)p.

Ontogenesis of alpha 2-adrenoceptor coupling with GTP-binding proteins in the rat telencephalon

The ontogenesis of alpha 2-adrenoceptors and GTP-binding proteins and their coupling activity were investigated in telencephalon 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.

Influences of pertussis toxin, guanine nucleotides and forskolin on adenylate cyclase in striatal membranes of infant, adult and senescent rats

To identify age-related changes in the dopamine (DA) receptors-GTP-binding protein-adenylate cyclase system, the following experiments were performed at 7 days (infant), 70 days (adult) and 2 years (senescent) in striatal membranes of rats: (1) effects of GTP in the presence and absence of pertussis toxin (islet-activating protein, IAP) on adenylate cyclase in the presence of forskolin alone, (2) the same in the presence of forskolin plus DA and (3) the corresponding effect of guanyl-5'-yl-beta, alpha-imido-diphosphate (GppNHp). GTP caused biphasic effects: the activation at 1 microM and the inhibition at 100 microM on forskolin-stimulated cyclase activity at 70 days. The inhibition was suppressed with IAP pretreatment. In infant membranes, 100 microM GTP inhibited the activity in the absence and presence of 100 microM DA and IAP induced a reversal from the inhibition to the stimulation only in the presence of DA. In senescent animals, neither GTP nor IAP affected the activity. GppNHp at 1, 10 and 100 microM only activated and did not inhibit forskolin-stimulated cyclase at each stage. GppNHp-caused stimulation was no more affected by IAP. IAP ADP-ribosylated 41,000 dalton proteins at each stage and the specific activity of ADP-ribosylation was not changed during development and aging. It is suggested that inhibitory GTP-binding protein (Gi) with molecular size of 41,000 dalton is involved in DA receptor-adenylate cyclase system whose function is low at infant stage and markedly decreased at senescent stage in rat striatal membranes.

Developmental changes of cerebral cortical [3H]clonidine binding in rats: influences of guanine nucleotide and cations

Cerebral cortical [3H]clonidine binding and influences of GTP and cations were investigated in developing rats. The results from Scatchard plots were compatible with the presence of two populations of binding sites [high-affinity binding (KD = 0.59 nM) and low-affinity binding (KD = 7.12 nM)] in 70-day-old rats but only high-affinity binding (KD = 0.27 nM) on day 1. Low-affinity binding was detectable on day 7. KD values in high- and low-affinity binding were not significantly changed during development after 7 days. Bmax of high-affinity binding reached a peak on day 15, and the value of low-affinity binding gradually increased with age. The addition of 10 microM GTP caused a significant reduction in Bmax of high-affinity binding after day 7. Neither KD nor Bmax of low-affinity binding was affected by 10 microM GTP during development. NaCl (10 and 100 mM) diminished the binding on days 7 and 70. MnCl2 (0.1 and 1.0 mM) markedly increased the binding on days 15 and 70 but not on day 7. It is suggested that: (1) single binding sites of alpha 2-adrenoceptors with higher affinity seem to be present on day 1; (2) low-affinity binding appears on day 7; (3) the number of high-affinity binding sites reaches a peak on day 15, followed by changes in populations of high-affinity as well as low-affinity sites without changing affinity; (4) the regulatory mechanism in alpha 2-receptors by guanine nucleotide reaches functional maturity between days 1 and 7; and (5) the involvement of Na+ and Mn2+ in alpha 2-receptor binding becomes functional by days 7 and 15, respectively.

Involvement of sulfhydryl groups in cerebral cortical [3H]clonidine binding in developing rats

The involvement of essential sulfhydryl groups in alpha 2-adrenoceptor function was investigated in the cerebral cortex of 7 and 70 day old rats. N-Ethylmaleimide (NEM) inhibited specific [3H]clonidine binding to cerebral cortical membranes in a concentration-dependent and biphasic manner in both infant and adult rats. The inhibitory effect of NEM was attenuated by simultaneous addition of dithiothreitol 30 microM and 1 mM, though dithiothreitol up to 1 mM did not affect the binding. p-Chloromercuriphenylsulfonic acid also caused a significant reduction in [3H]clonidine binding at both stages. Scatchard analysis of [3H]clonidine binding showed that NEM 10 and 100 microM caused a significant decrease in Bmax of high affinity binding sites without changing KD. Neither Bmax nor KD values were changed by NEM 10 and 100 microM in low affinity sites. The treatment with NEM 10 and 100 microM significantly reduced the increase of binding induced by Mn2+ 10 and 100 microM which was observed on day 70 but not on day 7. It is suggested that two distinct categories of essential sulfhydryl groups are involved in cerebral cortical alpha 2-adrenoceptors and are functionally mature by day 7. Furthermore, sulfhydryl groups are involved in the Mn2+-induced increase of alpha 2-receptors in adult rats.