Changes in G protein expression account for impaired modulation of hepatic cAMP formation after BDL.

The regulation of cAMP synthesis by hormones and bile acids is altered in isolated hamster hepatocytes 2 days after bile duct ligation (BDL) [Y. Matsuzaki, B. Bouscarel, M. Le, S. Ceryak, T. W. Gettys, J. Shoda, and H. Fromm. Am. J. Physiol. 273 ( Gastrointest. Liver Physiol. 36): G164-G174, 1997]. Therefore, studies were undertaken to elucidate the mechanism(s) responsible for this impaired modulation of cAMP formation. Hepatocytes were isolated 48 h after either a sham operation or BDL. Both preparations were equally devoid of cholangiocyte contamination. Although the basal cAMP level was not affected after BDL, the ability of glucagon to maximally stimulate cAMP synthesis was decreased by ∼40%. This decreased glucagon effect after BDL was not due to alteration of the total glucagon receptor expression. However, this effect was associated with a parallel 50% decreased expression of the small stimulatory G protein α-subunit (GsαS). The expression of either the large subunit (GsαL) or the common β-subunit remained unchanged. The expression of Giα2and Giα3was also decreased by 25 and 46%, respectively, and was associated with the failure of ANG II to inhibit stimulated cAMP formation. Therefore, alterations of the expression of GsαSand Giα are, at least in part, responsible for the attenuated hormonal regulation of cAMP synthesis. Because cAMP has been reported to stimulate both bile acid uptake and secretion, impairment of cAMP synthesis and bile acid uptake may represent an initial hepatocellular defense mechanism during cholestasis.

[1]  Y. Matsuzaki,et al.  Effect of cholestasis on regulation of cAMP synthesis by glucagon and bile acids in isolated hepatocytes. , 1997, American Journal of Physiology.

[2]  J. Amos-Landgraf,et al.  Age-related changes in G proteins in rat aorta. , 1996, The journals of gerontology. Series A, Biological sciences and medical sciences.

[3]  R. B. Merrifield,et al.  Antibodies against specific extracellular epitopes of the glucagon receptor block glucagon binding. , 1996, Proceedings of the National Academy of Sciences of the United States of America.

[4]  T. Yagami.  Differential coupling of glucagon and beta-adrenergic receptors with the small and large forms of the stimulatory G protein. , 1995, Molecular pharmacology.

[5]  F. Noonan,et al.  Alteration of cAMP-mediated hormonal responsiveness by bile acids in cells of nonhepatic origin. , 1995, The American journal of physiology.

[6]  R. Surwit,et al.  Tissue-specific alterations in G protein expression in genetic versus diet-induced models of non-insulin-dependent diabetes mellitus in the mouse. , 1995, Metabolism: clinical and experimental.

[7]  T. Gettys,et al.  Ursodeoxycholic acid inhibits glucagon-induced cAMP formation in hamster hepatocytes: a role for PKC. , 1995, The American journal of physiology.

[8]  Howard M. Dubner,et al.  The role of sodium in the uptake of ursodeoxycholic acid in isolated hamster hepatocytes , 1995, Hepatology.

[9]  H. Kim,et al.  Synthesis and expression of a gene for the rat glucagon receptor. Replacement of an aspartic acid in the extracellular domain prevents glucagon binding. , 1994, The Journal of biological chemistry.

[10]  A. Couvineau,et al.  G proteins in rat liver proliferation during cholestasis , 1994, Hepatology.

[11]  J. Raymond,et al.  Cell-specific physical and functional coupling of human 5-HT1A receptors to inhibitory G protein alpha-subunits and lack of coupling to Gs alpha. , 1993, Biochemistry.

[12]  B. Dixon,et al.  Distribution of adenylate cyclase and GTP-binding proteins in hepatic plasma membranes. , 1993, American Journal of Physiology.

[13]  M. Anwer,et al.  Role of intracellular calcium and protein kinases in the activation of hepatic Na+/taurocholate cotransport by cyclic AMP. , 1993, The Journal of biological chemistry.

[14]  D. Larrouy,et al.  Coupling of the alpha 2-adrenergic receptor to the inhibitory G-protein Gi and adenylate cyclase in HT29 cells. , 1993, The Biochemical journal.

[15]  G. Alpini,et al.  Secretin stimulates bile ductular secretory activity through the cAMP system. , 1992, The American journal of physiology.

[16]  Hsien-yu Wang,et al.  Antisense oligodeoxynucleotides to Gs protein α-subunit sequence accelerate differentiation of fibroblasts to adipocytes , 1992, Nature.

[17]  T. Palmer,et al.  Determination of G-protein levels, ADP-ribosylation by cholera and pertussis toxins and the regulation of adenylyl cyclase activity in liver plasma membranes from lean and genetically diabetic (db/db) mice. , 1991, Biochimica et biophysica acta.

[18]  E. Feytmans,et al.  Compartmental analysis of steady‐state taurocholate transport kinetics by isolated rat hepatocytes , 1991, Hepatology.

[19]  Y. Kawai,et al.  Ontogeny of guanine-nucleotide-binding regulatory proteins in rabbit liver. , 1991, The Biochemical journal.

[20]  H. Cantiello,et al.  G alpha i-3 regulates epithelial Na+ channels by activation of phospholipase A2 and lipoxygenase pathways. , 1990, The Journal of biological chemistry.

[21]  V. Hruby,et al.  Hormonal regulation of Gi2 α-subunit phosphorylation in intact hepatocytes , 1990 .

[22]  N. LaRusso,et al.  Isolation and morphologic characterization of bile duct epithelial cells from normal rat liver. , 1989, Gastroenterology.

[23]  R. Wange,et al.  Guanine nucleotide binding regulatory proteins and adenylate cyclase in livers of streptozotocin- and BB/Wor-diabetic rats. Immunodetection of Gs and Gi with antisera prepared against synthetic peptides. , 1989, The Journal of clinical investigation.

[24]  J. Jauniaux,et al.  The cyclic AMP-mediated stimulation of cell proliferation. , 1989, Trends in biochemical sciences.

[25]  L. Lumeng,et al.  Effect of glucagon on hepatic taurocholate uptake: relationship to membrane potential. , 1985, The American journal of physiology.

[26]  J. Schölmerich,et al.  Loss of glucagon control of gluconeogenesis in liver cells from rats with bile duct obstruction. , 1985, Biochemical and biophysical research communications.

[27]  S. Bellentani,et al.  Specificity of an Na+ -dependent taurocholate transport site in isolated rat hepatocytes. , 1984, The American journal of physiology.

[28]  P. Blackmore,et al.  Vasopressin-, angiotensin II-, and alpha 1-adrenergic-induced inhibition of Ca2+ transport by rat liver plasma membrane vesicles. , 1984, The Journal of biological chemistry.

[29]  P. Insel,et al.  Regulation of adenylate cyclase of human platelet membranes by forskolin. , 1982, The Journal of biological chemistry.

[30]  J. Daly,et al.  Forskolin: unique diterpene activator of adenylate cyclase in membranes and in intact cells. , 1981, Proceedings of the National Academy of Sciences of the United States of America.

[31]  J. Hanoune,et al.  The adenylate cyclase system in human liver: characterization, subcellular distribution and hormonal sensitivity in normal or cirrhotic adult, and in foetal liver. , 1979, Clinical science.

[32]  R. Sherwin,et al.  Hyperglucagonemia in cirrhosis: Altered secretion and sensitivity to glucagon , 1978 .

[33]  J. Barnhart,et al.  Characteristics Common to Choleretic Increments of Bile Induced by Theophylline, Glucagon and SQ-20009 in the dog 1 , 1975, Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine.

[34]  M. Johnson,et al.  The regulation of gluconeogenesis in isolated rat liver cells by glucagon, insulin, dibutyryl cyclic adenosine monophosphate, and fatty acids. , 1972, The Journal of biological chemistry.

[35]  J. Boyer,et al.  Down-regulation of expression and function of the rat liver Na+/bile acid cotransporter in extrahepatic cholestasis. , 1996, Gastroenterology.

[36]  T. Gettys,et al.  Examination of relative rates of cAMP synthesis and degradation in crude membranes of adipocytes treated with hormones. , 1990, Second messengers and phosphoproteins.

[37]  H. Bourne,et al.  Genetic deficiency of the alpha subunit of the guanine nucleotide-binding protein Gs as the molecular basis for Albright hereditary osteodystrophy. , 1988, Proceedings of the National Academy of Sciences of the United States of America.

[38]  A. Gilman,et al.  G proteins: transducers of receptor-generated signals. , 1987, Annual review of biochemistry.

[39]  G. Milligan,et al.  Abolition of the expression of inhibitory guanine nucleotide regulatory protein Gi activity in diabetes , 1987, Nature.

[40]  A. Gilman.  Guanine nucleotide-binding regulatory proteins and dual control of adenylate cyclase. , 1984, The Journal of clinical investigation.

[41]  C. L. Oakley,et al.  Ligation of the common bile duct , 1932 .