Hepatocyte beta-adrenergic responsiveness and guanine nucleotide-binding regulatory proteins

1989 ◽  
Vol 256 (2) ◽  
pp. C384-C389 ◽  
Author(s):  
J. A. Garcia-Sainz ◽  
M. E. Huerta-Bahena ◽  
C. C. Malbon
Keyword(s):  
Binding Protein ◽  
Nucleotide Binding ◽  
Regulatory Proteins ◽  
Guanine Nucleotide ◽  
Guanine Nucleotide Binding Protein ◽  
Beta Adrenergic ◽  
Adp Ribosylation ◽  
Liver Membranes ◽  
Guanine Nucleotide Binding ◽  
Nucleotide Binding Protein

Hepatocytes isolated from hypothyroid, adrenalectomized, or partially hepatectomized rats display an enhanced beta-adrenergic responsiveness as compared with cells from control animals. The enhanced beta-adrenergic responsiveness is evidenced by both increased ureagenesis and adenosine 3',5'-cyclic monophosphate (cAMP) accumulation in response to isoproterenol. The role of stimulatory guanine nucleotide-binding protein (Gs) and inhibitory guanine nucleotide-binding protein (Gi) in the enhanced responsiveness was studied. It was observed, contrary to what would have been anticipated, that the level of Gs [as reflected by cholera toxin-catalyzed ADP ribosylation, 5'-guanosine gamma-thiotriphosphate (GTP gamma S)-stimulated adenylate cyclase activity, and a functional reconstitution assay] was decreased in liver membranes from adrenalectomized and partially hepatectomized rats as compared with the controls. Furthermore, the level of Gi was increased in these conditions as reflected by pertussis toxin-catalyzed ADP ribosylation. The data suggest that changes in beta-adrenergic receptor levels rather than the levels of guanine nucleotide-binding (G) regulatory proteins predominate in regulation of hepatic beta-adrenergic responses by hypothyroidism, adrenalectomy, or partial hepatectomy.

scholarly journals Cholera toxin treatment produces down-regulation of the α-subunit of the stimulatory guanine-nucleotide-binding protein (Gs)

1989 ◽  
Vol 262 (2) ◽  
pp. 643-649 ◽  
Author(s):  
G Milligan ◽  
C G Unson ◽  
M J Wakelam
Keyword(s):  
Plasma Membrane ◽  
Cholera Toxin ◽  
Binding Protein ◽  
Nucleotide Binding ◽  
Guanine Nucleotide ◽  
Down Regulation ◽  
Guanine Nucleotide Binding Protein ◽  
Adp Ribosylation ◽  
Guanine Nucleotide Binding ◽  
Nucleotide Binding Protein

The effect of activation of the alpha-subunit(s) of the stimulatory guanine-nucleotide-binding protein, Gs, on levels of this polypeptide(s) associated with the plasma membrane of L6 skeletal myoblasts was ascertained. Incubation of these cells with cholera toxin led to a time- and concentration-dependent ‘down-regulation’ of both 44 and 42 kDa forms of Gs alpha as assessed by immunoblotting with an anti-peptide antiserum (CS1) able to identify the extreme C-terminus of Gs. The effect of cholera toxin was specific for Gs; levels of Gi alpha in membranes of cholera toxin-treated cells were not different from untreated cells. Down-regulation of Gs was absolutely dependent upon prior ADP-ribosylation, and hence activation of Gs and was not mimicked by other agents which elevate intracellular levels of cyclic AMP. Pretreatment with pertussis toxin, which catalyses ADP-ribosylation of Gi but not of Gs, did not down-regulate either Gi or Gs, demonstrating that covalent modification by ADP-ribosylation is alone not a signal for removal of G-proteins from the plasma membrane.

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