scholarly journals N 6-(Phenylisopropyl)adenosine prevents glucagon both blocking insulin's activation of the plasma-membrane cyclic AMP phosphodiesterase and uncoupling hormonal stimulation of adenylate cyclase activity in hepatocytes

1984 ◽  
Vol 222 (1) ◽  
pp. 177-182 ◽  
Author(s):  
A V Wallace ◽  
C M Heyworth ◽  
M D Houslay
Keyword(s):  
Plasma Membrane ◽  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Phosphodiesterase Inhibitor ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Maximal Effect ◽  
Hormonal Stimulation ◽  
Cyclic Amp Phosphodiesterase ◽  
Phenylisopropyl Adenosine

Glucagon (10nM) prevented insulin (10nM) from activating the plasma-membrane cyclic AMP phosphodiesterase. This effect of glucagon was abolished by either PIA [N6-(phenylisopropyl)adenosine] (100nM) or adenosine (10 microM). Neither PIA nor adenosine exerted any effect on the plasma-membrane cyclic AMP phosphodiesterase activity either alone or in combination with glucagon. Furthermore, PIA and adenosine did not potentiate the action of insulin in activating this enzyme. 2-Deoxy-adenosine (10 microM) was ineffective in mimicking the action of adenosine. The effect of PIA in preventing the blockade by glucagon of insulin's action was inhibited by low concentrations of theophylline. Half-maximal effects of PIA were elicited at around 6nM-PIA. It is suggested that adenosine is exerting its effects on this system through an R-type receptor. This receptor does not appear to be directly coupled to adenylate cyclase, however, as PIA did not affect either the activity of adenylate cyclase or intracellular cyclic AMP concentrations. Insulin's activation of the plasma-membrane cyclic AMP phosphodiesterase, in the presence of both glucagon and PIA, was augmented by increasing intracellular cyclic AMP concentrations with either dibutyryl cyclic AMP or the cyclic AMP phosphodiesterase inhibitor Ro-20-1724. PIA also inhibited the ability of glucagon to uncouple (desensitize) adenylate cyclase activity in intact hepatocytes. This occurred at a half-maximal concentration of around 3 microM-PIA. However, if insulin (10 nM) was also present in the incubation medium, PIA exerted its action at a much lower concentration, with a half-maximal effect occurring at around 4 nM.

scholarly journals Extracellular calcium modulates insulin's action on enzymes controlling cyclic AMP metabolism in intact hepatocytes

1993 ◽  
Vol 293 (1) ◽  
pp. 249-253 ◽  
Author(s):  
F Irvine ◽  
A V Wallace ◽  
S R Sarawak ◽  
M D Houslay
Keyword(s):  
Plasma Membrane ◽  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Incubation Medium ◽  
Extracellular Calcium ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Cyclic Amp Phosphodiesterase ◽  
Peripheral Plasma ◽  
Incubation Buffer

Absence of physiological concentrations of extracellular Ca2+ in the Krebs-Henseleit incubation buffer did not affect the ability of 10 nM glucagon (< 5%) to increase hepatocyte intracellular cyclic AMP concentrations, but severely ablated (by approximately 70%) the ability of 10 nM insulin to decrease these elevated concentrations. Cyclic AMP metabolism is determined by production by adenylate cyclase and degradation by cyclic AMP phosphodiesterase (PDE). In the absence of added extracellular Ca2+ (2.5 mM), insulin's ability to activate PDE activity was selectively compromised, showing a failure of insulin to activate two of the three insulin-stimulated activities, namely the ‘dense-vesicle’ and peripheral plasma-membrane (PPM) PDEs. In the absence of added Ca2+, insulin's ability to inhibit adenylate cyclase activity in intact hepatocytes was decreased dramatically. Vasopressin and adrenaline (+ propranolol) failed to elicit the activation of either the ‘dense-vesicle’ or the PPM-PDEs. The presence of physiological concentrations of extracellular Ca2+ in the incubation medium is shown to be important for the appropriate generation of insulin's actions on cyclic AMP metabolism.

scholarly journals Resensitization of hepatocyte glucagon-stimulated adenylate cyclase can be inhibited when cyclic AMP phosphodiesterase inhibitors are used to elevate intracellular cyclic AMP concentrations to supraphysiological values

1988 ◽  
Vol 249 (2) ◽  
pp. 543-547 ◽  
Author(s):  
G J Murphy ◽  
M D Houslay
Keyword(s):  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Phosphodiesterase Inhibitor ◽  
Phosphodiesterase Inhibitors ◽  
Maximal Effect ◽  
Cyclic Amp Phosphodiesterase ◽  
Dose Dependent Fashion ◽  
Independent Process ◽  
Pre Treatment ◽  
Dose Dependent

Treatment of intact hepatocytes with glucagon led to the rapid desensitization of adenylate cyclase, which reached a maximum around 5 min after application of glucagon, after which resensitization ensued. Complete resensitization occurred some 20 min after the addition of glucagon. In hepatocytes which had been preincubated with the cyclic AMP phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX), glucagon elicited a stable desensitized state where resensitization failed to occur even 20 min after exposure of hepatocytes to glucagon. Treatment with IBMX alone did not elicit desensitization. The action of IBMX in stabilizing the glucagon-mediated desensitized state was mimicked by the non-methylxanthine cyclic AMP phosphodiesterase inhibitor Ro-20-1724 [4-(3-butoxy-4-methoxylbenzyl)-2-imidazolidinone]. IBMX inhibited the resensitization process in a dose-dependent fashion with an EC50 (concn. giving 50% of maximal effect) of 26 +/- 5 microM, which was similar to the EC50 value of 22 +/- 6 microM observed for the ability of IBMX to augment the glucagon-stimulated rise in intracellular cyclic AMP concentrations. Pre-treatment of hepatocytes with IBMX did not alter the ability of either angiotensin or the glucagon analogue TH-glucagon, ligands which did not increase intracellular cyclic AMP concentrations, to cause the rapid desensitization and subsequent resensitization of adenylate cyclase. It is suggested that, although desensitization of glucagon-stimulated adenylate cyclase is elicited by a cyclic AMP-independent process, the resensitization of adenylate cyclase can be inhibited by a process which is dependent on elevated cyclic AMP concentrations. This action can be detected by attenuating the degradation of cyclic AMP by using inhibitors of cyclic AMP phosphodiesterase.

scholarly journals Regulation of adenylate cyclase and cyclic AMP phosphodiesterase by 5-hydroxytryptamine and calcium ions in blowfly salivary-gland homogenates

1982 ◽  
Vol 204 (1) ◽  
pp. 153-159 ◽  
Author(s):  
I Litosch ◽  
M Fradin ◽  
M Kasaian ◽  
H S Lee ◽  
J N Fain
Keyword(s):  
Salivary Gland ◽  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Guanine Nucleotides ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Cyclic Amp Phosphodiesterase ◽  
Maximal Stimulation ◽  
Increased Activity ◽  
Stimulation Of

Salivary-gland homogenates contain 5-hydroxytryptamine-stimulated adenylate cyclase. Half-maximal stimulation was obtained with 0.1 microM-5-hydroxytryptamine in the presence of added guanine nucleotides. Gramine antagonized the stimulation of cyclase caused by 5-hydroxytryptamine. In the presence of hormone, guanosine 5′-[gamma-thio]triphosphate produced a marked activation of adenylate cyclase activity. Stimulation of adenylate cyclase by forskolin or fluoride did not require the addition of guanine nucleotides or hormone. In the presence of EGTA, Ca2+ produced a biphasic activation of cyclase activity. Ca2+ at 1-100 microM increased activity, whereas 2000 microM-Ca2+ inhibited cyclase activity. The neuroleptic drugs trifluoperazine and chlorpromazine non-specifically inhibited adenylate cyclase activity even in the absence of Ca2+. The cyclic AMP phosphodiesterase activity in homogenates was not affected by Ca2+ or exogenous calmodulin. This enzyme was also inhibited by trifluoperazine in the absence of Ca2+. These results indicate that Ca2+ elevates adenylate cyclase activity, but had no effect on cyclic AMP phosphodiesterase of salivary-gland homogenates.

Acetylcholine inhibits positive inotropic effect of cholera toxin in ventricular muscle

1982 ◽  
Vol 243 (3) ◽  
pp. H434-H441
Author(s):  
A. J. Pappano ◽  
P. M. Hartigan ◽  
M. D. Coutu
Keyword(s):  
Chick Embryo ◽  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Cholera Toxin ◽  
Positive Inotropic Effect ◽  
Phosphodiesterase Inhibitor ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Inotropic Effect ◽  
Cyclic Monophosphate

Acetylcholine (ACh, 10(-6) M) had no effect on basal adenylate cyclase activity (3.4 +/- 0.56 pmol cyclic AMP . min-1 . mg wet wt-1), adenosine 3',5'-cyclic monophosphate (cyclic AMP) content (0.88 +/- 0.09 pmol/mg wet wt), or the force of contraction in paced (2.5 Hz) chick embryo right ventricles superfused with Tyrode solution. After 60-180 min of superfusion in the presence of cholera toxin (5 x 10(-6) g/ml), adenylate cyclase activity (1.7 times), cyclic AMP content (2.4 times), and contractility (2.4 times) had increased significantly above basal levels. ACh reversed the positive inotropic effect of cholera toxin but did not change the increased activity of adenylate cyclase and content of cyclic AMP obtained in cholera toxin. Stimulation of adenylate cyclase by isoproterenol (ISO) was inhibited by ACh in the absence and presence of cholera toxin. ACh did not change guanosine 3',5'-cyclic monophosphate (cyclic GMP) content in the absence or presence of cholera toxin. Cholera toxin has actions on chick embryo ventricle similar to those of the beta-adrenergic agonist, ISO, and the phosphodiesterase inhibitor, isobutylmethylxanthine. The ability of ACh to reverse the positive inotropic effect of cholera toxin without preventing the accumulation of cyclic AMP may involve the prevention or reversal of cyclic AMP-dependent phosphorylation. In this regard, reduction of Ca2+ influx through voltage-sensitive membrane channels may be an essential component of muscarinic inhibition.

Cytochemical Evidence for Presynatic β-Adrenergic Regulation of Secretion in the Developing Rat Submandibular Gland

1977 ◽  
Vol 35 ◽  
pp. 430-431
Author(s):  
L.S. Cutler
Keyword(s):  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Submandibular Gland ◽  
Neonatal Rat ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Parotid Glands ◽  
Adrenergic Agonist ◽  
Rat Submandibular Gland

Many studies previously have shown that the B-adrenergic agonist isoproterenol and the a-adrenergic agonist norepinephrine will stimulate secretion by the adult rat submandibular (SMG) and parotid glands. Recent data from several laboratories indicates that adrenergic agonists bind to specific receptors on the secretory cell surface and stimulate membrane associated adenylate cyclase activity which generates cyclic AMP. The production of cyclic AMP apparently initiates a cascade of events which culminates in exocytosis. During recent studies in our laboratory it was observed that the adenylate cyclase activity in plasma membrane fractions derived from the prenatal and early neonatal rat submandibular gland was retractile to stimulation by isoproterenol but was stimulated by norepinephrine. In addition, in vitro secretion studies indicated that these prenatal and neonatal glands would not secrete peroxidase in response to isoproterenol but would secrete in response to norepinephrine. In contrast to these in vitro observations, it has been shown that the injection of isoproterenol into the living newborn rat results in secretion of peroxidase by the SMG (1).

Fluctuations of adenylate cyclase activity during anterior regeneration in Owenia fusiformis (Polychaete Annelid)

Development ◽  
1978 ◽  
Vol 48 (1) ◽  
pp. 73-78
Author(s):  
Josiane Coulon ◽  
Monique Marilley
Keyword(s):  
Cell Cycle ◽  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Biochemical Assays ◽  
Strong Stimulation ◽  
Periodic Fluctuations ◽  
Early Phases ◽  
Anterior Regeneration

Biochemical assays of adenylate cyclase activity were performed during the early phases of regeneration in Owenia fusiformis (Polychaete Annelid). The results indicate the existence of a strong stimulation in an early phase following trauma. This stimulation is then followed by periodic fluctuations exhibiting a diurnal rhythm correlated with the cell cycle. Adenylate cyclase activity is also shown to be neurotransmitter-dependent. In this paper it is proposed that neurotransmitters might participate in the regulation of cyclic AMP formation, by means of adenylate cyclase acting on target blastema cells, undergoing the cell cycle.

scholarly journals Forskolin refractoriness. Exposure to the diterpene alters guanine nucleotide-dependent adenylate cyclase and calcium-uptake activity of cells cultured from the rat aorta

1987 ◽  
Vol 241 (2) ◽  
pp. 463-467 ◽  
Author(s):  
J F Krall ◽  
N Jamgotchian
Keyword(s):  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Cultured Cells ◽  
Rat Aorta ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Morphological Properties ◽  
Guanine Nucleotide ◽  
Intact Cells ◽  
Uptake Activity

Cells with the morphological properties of endothelial cells were cultured from the rat aorta. The cultured cells accumulated 45Ca2+ from the medium in a manner which was stimulated by forskolin and by 8-bromo-cyclic AMP. Pretreating the cultures for 20 h with forskolin diminished forskolin-dependent Ca2+-uptake activity. Adenylate cyclase activity of cultured cell homogenates was stimulated by guanosine 5′-[beta, gamma-imido]triphosphate (p[NH]ppG) and forskolin, and by isoprenaline in the presence, but not in the absence, of guanine nucleotide. p[NH]ppG increased forskolin sensitivity and caused a leftward shift in the forskolin dose-response curve. Pretreating the cultured cells with forskolin for 20 h, conditions that decreased forskolin-dependent Ca2+ uptake, increased basal and guanine nucleotide-dependent adenylate cyclase activity, but not forskolin-dependent activity determined in the absence of p[NH]ppG. Forskolin pretreatment diminished p[NH]ppG's capacity to increase forskolin sensitivity, but did not have a significant effect on either the sensitivity of adenylate cyclase to p[NH]ppG or its responsiveness to isoprenaline. These results suggest that the Ca2+-uptake mechanism is cyclic AMP-dependent and that guanine nucleotides mediated forskolin-dependent cyclic AMP production by the intact cells. In addition, there may be different guanine nucleotide requirements for hormone-receptor coupling and forskolin activation.

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