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At least 865 records · Page 48Linked to original sources
PubMed1991

Cholera toxin and Gs protein modulation of synaptic transmission in guinea pig mesenteric artery.

Cholera toxin (CTX) was used to test whether the presynaptic beta-adrenoceptors of guinea-pig mesenteric artery are coupled via stimulatory GTP-binding proteins. The vascular smooth muscle cells were electrically quiescent unless stimulated and had a mean resting potential of -68.7 +/- 2.8 mV (n = 16) and input resistance of 12.1 +/- 0.5 M omega (n = 4). Perivascular nerve stimulation with brief square pulses evoked excitatory junction potentials (EJPs) in the muscle cells. Isoproterenol (0.1 microM) enhanced the EJP amplitude without modifying the passive membrane properties of the muscle cells. The beta-blocker, propranolol (0.5 microM), prevented the effects of isoproterenol on EJP amplitude. The permeant analogue of cyclic AMP, 8-bromocAMP, also potentiated EJP amplitude. EJP amplitude was markedly enhanced by treatment of the isolated blood vessels with CTX (10 micrograms/ml for 1 h). The muscle cells became hyperpolarized (-74.6 +/- 2.1 mV, n = 5), and their input resistances were significantly reduced (8.2 +/- 0.5 M omega, n = 4). These effects of CTX persisted after washout. Addition of GM1 ganglioside (5 micrograms/ml) prevented the CTX effects. The CTX enhancement of EJP amplitude was not prevented by application of depolarizing current (ca. 0.5 nA) the muscle cells (to counter the hyperpolarization). These results suggest that CTX increases the neurotransmitter release from the nerve terminals; the hyperpolarization may be due to an increase in K+ conductance. These effects of CTX may be mainly due to elevation of cAMP in the nerve terminal and in the muscle cell.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1989

Forskolin inhibits the Gs-stimulated adenylate cyclase in rat ascites hepatoma AH66F cells.

Forskolin increased intracellular cyclic AMP and augmented cyclic AMP formation by prostaglandin E1 (PGE1) in normal rat hepatocytes and ascites hepatoma AH66 cells. However, in AH66F cells which were derived from the AH66 cell line, the diterpene only slightly increased the cyclic AMP level, and dose-dependently inhibited the accumulation caused by PGE1. Forskolin dose-dependently activated adenylate cyclase in these membranes, and the magnitude of activation by forskolin was largest in the following order: hepatocytes, AH66 cells, and AH66F cells. This difference may be based on the number of forskolin-binding sites. The binding affinity of forskolin for each cell membrane was similar. The number and affinity of forskolin-binding sites in these cells were not influenced by 5'-guanylylimidodiphosphate [Gpp(NH)p]. In hepatocytes and AH66 cells, forskolin and other adenylate cyclase activators such as PGE1, GTP, Gpp(NH)p, F-, and Mn2+ synergistically increased the enzyme activity. In AH66F cells, the forskolin-stimulated activity was hardly influenced by the GTP analog, and forskolin diminished the activities induced by the GTP analog in a manner similar to that of diterpene alone. Forskolin (10 microM) also significantly inhibited the activities induced by PGE1, GTP, and F-. The effect of forskolin with Mn2+ was additive in AH66F cells. The data suggest that forskolin promotes the interaction between the stimulatory guanine nucleotide-binding protein and the catalytic unit in the membrane of normal hepatocytes and AH66 cells, but it interferes with the coupling in AH66F cells.

Adenylyl Cyclases↗
PubMed1989

Mapping of beta-adrenoceptor coupling domains to Gs-protein by site-specific synthetic peptides.

Peptides corresponding to the known sequence of turkey erythrocyte beta 1-adrenergic receptor were synthesized and the effects on receptor-mediated cyclase activation were measured. Peptides corresponding to the first and second intracellular loops (T61-71 and T138-159) inhibited at micromolar concentrations the hormone-dependent cyclase activation in turkey erythrocyte membranes. In contrast, the peptide corresponding to the C-terminal part of the third intracellular loop (T284-295) increased the cyclase activity in a hormone-independent manner. Peptides T338-353 and T2-10 and a number of synthetic peptides unrelated to the beta-adrenoceptor had no effect.

Adenylyl Cyclases↗
PubMed1991

Phorbol-ester-induced phosphorylation of the beta 2-adrenergic receptor decreases its coupling to Gs.

Phorbol-esters have been shown to modulate the beta-adrenergic-stimulated adenylyl cyclase in a number of cell lines. Here, using site directed mutagenesis, we investigate the role of the beta 2-adrenergic receptor phosphorylation by protein kinase C in this regulatory process. Mutation of the serine-261, -262, -344 and -345 of the beta 2-adrenergic receptor prevented the phorbol-ester-induced phosphorylation of the receptor. This mutation also abolished the phorbol-ester-induced decrease in high-affinity agonist binding and potency of the beta 2-adrenergic receptor. We suggest that protein kinase C mediated phosphorylation of the receptor promotes its functional uncoupling.

Adenylyl Cyclases↗
PubMed1990

Cytoplasmic microinjection of immunoglobulin Gs recognizing RNA helices inhibits human cell growth.

We report here that nucleolar and cytoplasmic RNA in mammalian cells is recognized specifically by both experimentally induced monoclonal IgG unique for left-handed Z-RNA and by autoimmune mouse monoclonal IgG specific for ribosomal RNA. Nucleolar Z-RNA synthesis, like nucleolar ribosomal RNA synthesis, is inhibited by actinomycin D treatment and dimethylsulfoxide-induced differentiation. Immune anti-Z-RNA IgGs microinjected into living nuclei bind nucleolar RNA, and these complexes appear to be removed from the nucleus within minutes. Cytoplasmically microinjected monoclonal or polyclonal anti-Z-RNA IgGs specifically bind cytoplasmic RNA and inhibit cell multiplication. Microinjection of antibodies directed against double-stranded RNAs. Elevated ionic conditions, which in energy-minimized models can cause the walls of the groove in Z-RNA (but not Z-DNA) to approach each other and close, also prevent antibody binding to specific synthetic or cellular Z-RNA determinants. Our antibodies binding unique Z-RNA structures probably recognize antigens determined by the exposed 2'-OH ribose sugar-phosphate groups.

Animals↗
PubMed1994

Activation and depalmitoylation of Gs alpha.

[3H]palmitate attached to mutationally activated alpha s (alpha s-R201C) turns over rapidly, compared with palmitate linked to normal alpha s (t1/2 approximately 2 min versus 90 min); although alpha s-R201C (unlike normal alpha s) is predominantly found in the cytosol, [3H]palmitate is linked only to the membrane-bound pool of alpha s, normal or mutant. Similarly, activation of wild-type alpha s by isoproterenol, a beta-adrenoceptor agonist that also induces membrane-to-cytosol translocation of alpha s, dramatically accelerates depalmitoylation of alpha s. Thus, activation-induced removal of palmitate provides an explanation for activation-induced shifts of alpha s to the cytosol. Regulated palmitoylation cycles provide a potential general mechanism for controlling reversible changes in the cellular location and activity of a protein.

Adrenergic beta-Agonists↗
PubMed1993

Control of IgG/Fc glycosylation: a comparison of oligosaccharides from chimeric human/mouse and mouse subclass immunoglobulin Gs.

Oligosaccharide profiles were obtained for chimeric mouse-human antibodies corresponding to each of the human IgG subclasses 1-4, and mouse IgG2b antibodies each expressed in the mouse J558L cell line. These antibodies have specificity for the NIP hapten and form a matched set of IgGs. An IgG4 chimeric antibody (B72.3) produced in the chinese hamster ovary (CHO-K1) cell line was also analysed for carbohydrate. Additionally aglycosylated mutants of this IgG4 (B72.3) and anti-NIP mouse IgG2b were analysed. The total lack of carbohydrate found in the aglycosylated site-directed mutants human chimeric IgG4 B72.3 (Asn 297-->Gln) and mouse IgG2b (Asn 297-->Ala) demonstrates that there are no N-glycosylation sites other than Asn 297. Therefore glycosylation profiles for all the IgGs analysed reflect carbohydrate attached to this site. Factors such as cell type (A), template direction by the IgG heavy chains (B) and culture conditions (C) are shown to influence IgG glycosylation profiles. (A) The anti-NIP IgG antibodies expressed by the J558L cell line may have one or two Gal (alpha 1-->3) Gal residues per oligosaccharide unit, indicative of the presence of (alpha 1-->3) galactosyl transferase in the J558L mouse cell line. (B) The galactosylation profiles obtained for the IgG heavy chains, in particular the preference for galactosylation of the Man (alpha 1-->6) arm rather than the Man (alpha 1-->3) arm, contrary to the beta-galactosyltransferase specificity, suggest that the polypeptide chain may act as a template to influence the extent of galactosylation and hence the proportions of each oligosaccharide incorporated. The IgG2 antibody does not display this galactosylation preference. (C) The extent of galactosylation appears to be influenced by the growth conditions, with the highest levels of galactosylation being found for IgG produced by cells grown in still cultures, rather than cells grown as ascites or in hollow fibre bioreactors. It is concluded that though the profile of glycosylation is controlled predominantly by the glycosylation activity of the cell in which the IgG is expressed, differences between the IgG heavy chain templates of the various subclasses and culture conditions can also influence glycosylation.

Animals↗
PubMed1995

Expression of glial fibrillary acidic protein (GFAP), glutamine synthetase (GS), and Bcl-2 protooncogene protein by Müller (glial) cells in retinal light damage of rats.

In retinal light damage, degeneration of photoreceptors may cause alterations of glial (Müller) cells. We performed immunocytochemical studies on Müller cells isolated from retinae of rats exposed to enhanced illumination for 24 months, a procedure which leads to complete loss of photoreceptor cells. One group of rats was fed daily with Ginkgo biloba extract (EGb 761, an established free radical-scavenger) during the last 8 months of life when the remaining photoreceptors (about 50%) die. We found that (1) Müller cells respond to photoreceptor damage by increased expression of glial fibrillary acidic protein, (2) Müller cells reduce expression of glutamine synthetase when the major glutamate-releasing neurons are lost, and (3) the application of exogenous free radical scavengers prevents the expression by Müller cells of the protooncogene protein Bcl-2, a molecule assumed to activate endogenous free radical-scavenging activities.

Animals↗