scholarly journals Structural specificity for prostaglandin effects on hepatocyte glycogenolysis

1990 ◽  
Vol 267 (1) ◽  
pp. 59-62 ◽  
Author(s):  
E P Brass ◽  
M J Garrity
Keyword(s):  
Glucose Metabolism ◽  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Plasma Membranes ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Sprague Dawley ◽  
Hepatic Glucose Metabolism ◽  
Sprague Dawley Rats ◽  
Cyclic Amp Accumulation

Prostaglandins (PGs) are known to have effects on hepatic glucose metabolism. Some actions of PGs in intact liver systems may not involve PG effects directly at the level of the hepatocyte. To define the ability of structurally distinct prostaglandins to affect hepatocyte metabolism directly, the regulation of glycogenolysis was studied in hepatocytes isolated from male Sprague-Dawley rats. PGF and PGB2 inhibited glucagon-stimulated glycogenolysis in the hepatocyte system. Pinane thromboxane A2 (PTA2) and PGD2 had no effect on glucagon-stimulated glycogenolysis. Consistent with their inhibition of glucagon-stimulated glycogenolysis, PGF2 and PGF2 alpha inhibited glucagon-stimulated hepatocyte cyclic AMP accumulation. These actions of PGB2 and PGF2 alpha are identical with those previously reported for PGE2. Additionally, PGE2, PGF2 alpha and PGB2 inhibited glucagon-stimulated adenylate cyclase activity in purified hepatic plasma membranes. In contrast, PGF2 alpha, PGD2 and PTA2 were all without affect on basal rates of hepatocyte glycogenolysis or hepatocyte cyclic AMP content. PGE2 also inhibited glycogenolysis stimulated by the alpha-adrenergic agonist phenylephrine. Exogenous arachidonic acid was not able to reproduce the affects of PGE2 or PGF2 alpha on hepatocyte glycogenolysis, consistent with an extra-hepatocyte source of the prostaglandins in the intact liver. Thus PGE2 and PGF2 alpha act specifically to inhibit glucagon-stimulated adenylate cyclase activity. No prostaglandin tested was found to stimulate glycogenolysis. PGE2 and PGF2 alpha may represent intra-hepatic modulators of hepatocyte glucose metabolism.

scholarly journals Bradykinin-dependent activation of adenylate cyclase activity and cyclic AMP accumulation in tracheal smooth muscle occurs via protein kinase C-dependent and -independent pathways

1994 ◽  
Vol 297 (1) ◽  
pp. 233-239 ◽  
Author(s):  
P A Stevens ◽  
S Pyne ◽  
M Grady ◽  
N J Pyne
Keyword(s):  
Smooth Muscle ◽  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Cholera Toxin ◽  
Phospholipase D ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Tracheal Smooth Muscle ◽  
Constitutive Activation ◽  
Cyclic Amp Accumulation

Treatment of cultured tracheal smooth-muscle cells (TSM) with phorbol 12-myristate 13-acetate (PMA) (100 nM) or bradykinin (100 nM) elicited enhanced basal and guanosine 5′-[beta gamma-imido]-triphosphate-stimulated adenylate cyclase activities in subsequently isolated membranes. Combined stimulation of cells was non-additive, indicating that both agents activate adenylate cyclase via similar routes. Both PMA (100 nM) and bradykinin (100 nM) allowed the alpha subunit of Gs to act as a more favourable substrate for its cholera-toxin-catalysed ADP-ribosylation in vitro. PMA was without effect on intracellular cyclic AMP in control cells. However, constitutive activation of Gs by treatment in vivo with cholera toxin (0.5 ng/ml, 18 h) sensitized the cells to PMA stimulation, resulting in a concentration-dependent increase in intracellular cyclic AMP accumulation (EC50 = 7.3 +/- 2.5 nM, n = 5). Bradykinin also elicited a concentration-dependent increase in intracellular cyclic AMP (EC50 = 63.3 +/- 14.5 nM, n = 3). Constitutive activation of Gs resulted in an increased maximal response (10-fold) and potency (EC50 = 6.17 +/- 1.6 nM, n = 3) to bradykinin. This response was not affected by the B2-receptor antagonist, NPC567 [which selectively blocks bradykinin-stimulated phospholipase C (PLC), with minor activity against phospholipase D (PLD) activity]. Des-Arg9-bradykinin (a B1-receptor agonist) was without activity. These results suggest that the receptor sub-type capable of activating PLD may also be stimulatory for cyclic AMP accumulation. Furthermore, pre-treatment of the cells with butan-l-ol (0.3%, v/v), which traps phosphatidate derived from PLD reactions, blocked the bradykinin-stimulated increase in intracellular cyclic AMP. These studies suggest that there may be a causal link between PLD-derived phosphatidate and the positive modulation of adenylate cyclase activity. In support of this, the concentration-dependence for bradykinin-stimulated adenylate cyclase activity was identical with that of bradykinin-stimulated phospholipase D activity (EC50 = 5 nM). Bradykinin, but not PMA, was also capable of eliciting the inhibition of cyclic AMP phosphodiesterase activity in TSM cells (EC50 > 100 nM) via an unidentified mechanism. These studies indicate that cross-regulation between the cyclic AMP pathway and phospholipid-derived second messengers in TSM cells does not occur as a consequence of PLC-catalysed PtdIns(4,5)P2 hydrolysis, but may involve, in part, PLD-catalysed phosphatidylcholine hydrolysis.

scholarly journals Resensitization of lutropin-desensitized tumour Leydig-cell adenylate cyclase with human erythrocyte membranes

1982 ◽  
Vol 204 (2) ◽  
pp. 613-616 ◽  
Author(s):  
C J Dix ◽  
B A Cooke
Keyword(s):  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Human Erythrocyte ◽  
Plasma Membranes ◽  
Control Cell ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Erythrocyte Membranes ◽  
Cell Plasma ◽  
Human Erythrocyte Membranes

Purified rat tumour Leydig cells were pretreated with or without lutropin (1 h at 32 degrees C). The plasma membranes were then isolated and the adenylate cyclase activity measured in the presence of freshly prepared or heat-inactivated (1 h at 60 degrees C) human erythrocyte membranes. In plasma membranes from control cells in the presence of heat-inactivated human erythrocyte membranes both guanosine 5'-[beta, gamma-imido]triphosphate (p[NH]ppG) plus lutropin and NaF caused a 45-50-fold increase in cyclic AMP production over 30 min compared with 12-13 fold p[NH[ppG and 2-3-fold with lutropin alone. In plasma membranes isolated from lutropin-pretreated cells the NaF- and the p[NH]ppG-stimulated cyclic AMP production rates were unchanged, but no effect of lutropin could be demonstrated with or without added p[NH]ppG. However, after mixing lutropin-desensitized Leydig tumour-cell plasma membranes with freshly prepared human erythrocyte plasma membranes, the adenylate cyclase activity in the presence of lutropin, p[NH]ppG, lutropin plus p[NH]ppG and NaF were similar to those of control cell plasma membranes treated in the same manner. The possible mechanisms of this reversal of lutropin-induced desensitization by human erythrocytes are discussed.

Interrelationships between PGE1 and PGI2 binding and stimulation of adenylate cyclase

1983 ◽  
Vol 244 (4) ◽  
pp. E367-E372 ◽  
Author(s):  
M. J. Garrity ◽  
K. R. Westcott ◽  
T. L. Eggerman ◽  
N. H. Andersen ◽  
D. R. Storm ◽  
...  
Keyword(s):  
Adenylate Cyclase ◽  
Binding Sites ◽  
Plasma Membranes ◽  
Membrane Receptors ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Enzyme Complex ◽  
Sprague Dawley ◽  
Rat Livers ◽  
Stimulation Of

The effects of prostaglandin E1 (PGE1) and prostacyclin (PGI2) on hepatic adenylate cyclase were studied in plasma membranes isolated from Sprague-Dawley rat livers. Both PGE1 and PGI2 stimulated this enzyme complex to the same maximal levels and with approximately the same EC50 (10(-7) M). Maximally stimulating concentrations of PGE1 and PGI2 were examined alone and together; their effects were not additive, indicating that the same enzyme complex was shared. Although a receptor for PGE1 could be demonstrated with a dissociation constant of 1 X 10(-8) M, PGI2 was only 1/100 as effective in competing for PGE1 binding sites (KD, 1 X 10(-6) M), indicating that these two prostaglandins may act via separate membrane receptors. PGI2 is known to be unstable at neutral pH; however, we have determined its half-life during these assays by a sensitive bioassay and concluded that the degradation of PGI2 is not sufficient to account for its inability to dissociate [3H]PGE1 binding. Further evidence that PGI2 might act through a distinct receptor was found in animals whose PGE1 receptors were 40% downregulated with a corresponding 28% decrease in PGE1-sensitive adenylate cyclase activity. These membranes had no such decrease in PGI2-sensitive adenylate cyclase activity. We conclude that 1) hepatic adenylate cyclase is equally sensitive to PGE1 and PGI2; 2) the same adenylate cyclase complex responds to both prostaglandins; and 3) PGE1 and PGI2 interact with separate membrane receptors in rat liver.

scholarly journals Islet-activating protein blocks glucagon desensitization in intact hepatocytes

1984 ◽  
Vol 222 (1) ◽  
pp. 189-194 ◽  
Author(s):  
C M Heyworth ◽  
E Hanski ◽  
M D Houslay
Keyword(s):  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Plasma Membranes ◽  
Regulatory Protein ◽  
Inhibitory Effect ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Inhibitory Input ◽  
Pronounced Increase ◽  
Guanine Nucleotide Regulatory Protein

Treatment of intact hepatocytes with islet-activating protein, from Bordatella pertussis, led to a pronounced increase in the ability of glucagon to raise intracellular cyclic AMP concentrations. Islet-activating protein, however, caused no apparent increase in the intracellular concentration of cyclic AMP under basal conditions. These effects were attributed to an enhanced ability of adenylate cyclase, in membranes from hepatocytes treated with islet-activating protein, to be stimulated by glucagon. When forskolin was used to amplify the basal adenylate cyclase activity, elevated GTP concentrations were shown to inhibit adenylate cyclase activity in membranes from control hepatocytes. This inhibitory effect of GTP was abolished if the hepatocytes had been pre-treated with islet activating protein. In isolated liver plasma membranes, islet-activating protein caused the NAD-dependent ribosylation of a Mr-40000 protein, the putative inhibitory guanine nucleotide regulatory protein, Ni. This effect was inhibited if guanosine 5′-[beta‐thio]diphosphate rather than GTP was present in the ribosylation incubations. The ability of glucagon to uncouple or desensitize the activity of adenylate cyclase in intact hepatocytes was also blocked by pre-treating hepatocytes with islet-activating protein. Islet-activating protein thus heightens the response of hepatocytes to the stimulatory hormone glucagon. It achieves this by both inhibiting the expression of desensitization and also removing a residual inhibitory input expressed in the presence of glucagon.

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