scholarly journals Role of Protein Phosphatases in Cyclic AMP-mediated Stimulation of Hepatic Na+/Taurocholate Cotransport

1998 ◽  
Vol 273 (45) ◽  
pp. 30039-30045 ◽  
Author(s):  
Sunil Mukhopadhyay ◽  
Cynthia R. L. Webster ◽  
M. Sawkat Anwer
Keyword(s):  
Cyclic Amp ◽  
Protein Phosphatases ◽  
Stimulation Of

scholarly journals The role of insulin in the modulation of glucagon-dependent control of phenylalanine hydroxylation in isolated liver cells

1987 ◽  
Vol 242 (3) ◽  
pp. 655-660 ◽  
Author(s):  
M J Fisher ◽  
A J Dickson ◽  
C I Pogson
Keyword(s):  
Cyclic Amp ◽  
Insulin Action ◽  
Phenylalanine Hydroxylase ◽  
Liver Cells ◽  
Phosphorylation State ◽  
Isolated Liver Cells ◽  
The Impact ◽  
Isolated Liver ◽  
Stimulation Of

The stimulation of phenylalanine hydroxylation in isolated liver cells by sub-maximally effective concentrations of glucagon (less than 0.1 microM) is antagonized by insulin (0.1 nM-0.1 microM). This phenomenon is a consequence of a decrease in the glucagon-stimulated phosphorylation of phenylalanine hydroxylase from liver cells incubated in the presence of insulin. The impact of insulin on the phosphorylation state and activity of the hydroxylase is mimicked by incubation of liver cells in the presence of orthovanadate (10 microM). A series of cyclic AMP and cyclic GMP analogues enhanced phenylalanine hydroxylation: in each case insulin diminished the stimulation of flux. These results are discussed in the light of the characteristics of insulin action on other metabolic processes.

Possible role of cyclic GMP in stimulus-secretion coupling by salt gland of the duck

1979 ◽  
Vol 237 (5) ◽  
pp. C200-C204 ◽  
Author(s):  
D. J. Stewart ◽  
J. Sax ◽  
R. Funk ◽  
A. K. Sen
Keyword(s):  
Cyclic Amp ◽  
Guanylate Cyclase ◽  
Cyclic Gmp ◽  
Salt Gland ◽  
Domestic Ducks ◽  
Stimulus Secretion Coupling ◽  
Stimulation Of

Stimulation of salt galnd secretion in domestic ducks in vivo increased the cyclic GMP concentration of the tissue, but had no effect on cyclic AMP levels. Methacholine, which is known to stimulate sodium transport by the glands both in vivo and in vitro, stimulated ouabain-sensitive respiration in salt gland slices. Cyclic GMP stimulated ouabain-sensitive respiration to the same extent as methacholine. Guanylate cyclase stimulators, hydroxylamine and sodium azide, also stimulated ouabain-sensitive respiration. The stimulation of ouabain-sensitive respiration by methacholine was blocked either by atropine or by removal of calcium from the incubation medium. The stimulation of ouabain-sensitive respiration by cyclic GMP still occurred in the absence of calcium. The above observations seem to indicate that cyclic GMP acts as a tertiary link in the process of stimulus-secretion coupling in the tissue.

Effect of lanthanum on the inotropic response of isoproterenol: role of the superficially bound calcium

1985 ◽  
Vol 63 (9) ◽  
pp. 1106-1112 ◽  
Author(s):  
Ahmad B. Fawzi ◽  
John H. McNeill
Keyword(s):  
Cyclic Amp ◽  
Positive Inotropic Effect ◽  
Direct Action ◽  
Maximum Response ◽  
Inotropic Response ◽  
Guinea Pig Heart ◽  
Low Concentrations ◽  
Stimulation Of ◽  
Calcium Pool

Mammalian myocardial contractility is believed to be related to the amount of calcium contained in a highly labile superficial calcium pool. The purpose of this study was to determine the role of such sites in the positive inotropic effect of isoproterenol. Lanthanum, an ion that is restricted to the extracellular space and that displaces the superficially bound calcium, was selected as a tool for this investigation. In Langendorff preparations of the guinea pig heart, lanthanum decreased the basal contractility index (+ dP/dtmax) in a concentration-dependent fashion (0.05–3μM) and blocked the inotropic response of isoproterenol in a noncompetitive manner (0.25–3 μM). Three-micromolar lanthanum (i) reduced basal contractility and the maximum response to isoproterenol by 97 and 95%, respectively, (ii) had no significant effect (p > 0.05) on basal and isoproterenol-induced cyclic AMP levels, and (iii) had no effect on the Kd of [3H]nitrendipine binding, but reduced the Bmax by 31%. While 1 μM lanthanum reduced basal contractility and the maximum response to isoproterenol by 90 and 70%, respectively, it had no effect on [3H]nitrendipine binding. These results suggest that the effects of such low concentrations of lanthanum (≤3 μM) are not related to a direct action on the calcium channels and are not mediated by an inhibition of isoproterenol stimulation of the enzyme adenylate cyclase. Therefore, one interpretation of these results suggests that superficially bound calcium is required for the inotropic response of isoproterenol.

Transepithelial Potential Changes During Stimulation of Isolated Salivary Glands with 5-Hydroxytryptamine and Cyclic Amp

1972 ◽  
Vol 56 (1) ◽  
pp. 139-153
Author(s):  
MICHAEL J. BERRIDGE ◽  
WILLIAM T. PRINCE
Keyword(s):  
Cyclic Amp ◽  
Salivary Glands ◽  
Electrical Response ◽  
Cation Transport ◽  
Anion Transport ◽  
Adenyl Cyclase ◽  
Positive Potential ◽  
Dose Dependent ◽  
Stimulation Of

1. The role of cyclic AMP in mediating the action of 5-HT on salivary glands has been studied by measuring transepithelial potentials. 2. The lumen of unstimulated glands is 4 mV positive but becomes 12 mV negative after treatment with 5-HT (10-8M). Both the potential and the secretory responses to 5-HT are dose-dependent over the same concentration range. 3. The electrical response of salivary glands to cyclic AMP is qualitatively different to that of 5-HT; instead of going negative the potential goes more positive. 4. An increase in positive potential is also observed after treatment with theophylline (10-2M), or when glands are stimulated with 5-HT in a chloride-free saline. 5. These results are consistent with the idea that 5-HT has two actions. One is to stimulate the enzyme adenyl cyclase to synthesize cyclic AMP, which, in turn, stimulates cation transport. The other is to increase anion transport by a mechanism which is independent of cyclic AMP.

Stimulation of ecdysteroidogenesis by small prothoracicotropic hormone: Role of cyclic AMP

1993 ◽  
Vol 92 (2) ◽  
pp. 221-228 ◽  
Author(s):  
R.D. Watson ◽  
W.E. Yeh ◽  
D.P. Muehleisen ◽  
C.J. Watson ◽  
W.E. Bollenbacher
Keyword(s):  
Cyclic Amp ◽  
Prothoracicotropic Hormone ◽  
Stimulation Of

Periodic stimuli are more successful than randomly spaced ones for inducing development in Dictyostelium discoideum

1988 ◽  
Vol 8 (6) ◽  
pp. 571-577 ◽  
Author(s):  
Vidyanand Nanjundiah
Keyword(s):  
Cyclic Amp ◽  
Dictyostelium Discoideum ◽  
Vegetative State ◽  
Terminal Differentiation ◽  
Cellular Slime Mold ◽  
Slime Mold Dictyostelium Discoideum ◽  
Cellular Slime ◽  
Per Se ◽  
Stimulation Of

Aggregation in the cellular slime mold Dictyostelium discoideum is due to chemotaxis. The chemoattractant, cyclic AMP, is synthesised and released periodically by the cells. Externally applied periodic pulses of cyclic AMP can also induce differentiation in this organism. The present work examines the role of periodicity per se in cyclic AMP-mediated stimulation of cell differentiation. For this purpose we use Agip53, a Dictyostelium mutant which does not develop beyond the vegetative state but can be made to aggregate and differentiate by reiterated applications of cyclic AMP. Importantly, Agip53 cells do not make or release any cyclic AMP themselves even in response to an increase in extracellular cyclic AMP. A comparison of the relative efficiencies of periodic and aperiodic stimulation shows that whereas the two patterns of stimulation are equally effective in inducing the formation of EDTA-stable cell contacts, periodic stimuli are significantly superior for inducing terminal differentiation. This suggests that there must be molecular pathways which can only function when stimulation occurs at regular intervals.

scholarly journals Role of fructose 2,6-bisphosphate in the stimulation of glycolysis by anoxia in isolated hepatocytes

1982 ◽  
Vol 206 (2) ◽  
pp. 359-365 ◽  
Author(s):  
L Hue
Keyword(s):  
Skeletal Muscle ◽  
Cyclic Amp ◽  
Adenine Nucleotides ◽  
Lactate Production ◽  
Isolated Hepatocytes ◽  
Anaerobic Glycolysis ◽  
Anaerobic Conditions ◽  
Effect Of Glucose ◽  
Stimulation Of

1. Incubation of hepatocytes from fed or starved rats with increasing glucose concentrations caused a stimulation of lactate production, which was further increased under anaerobic conditions. 2. When glycolysis was stimulated by anoxia, [fructose 2,6-bis-phosphate] was decreased, indicating that this ester could not be responsible for the onset of anaerobic glycolysis. In addition, the effect of glucose in increasing [fructose 2,6-bisphosphate] under aerobic conditions was greatly impaired in anoxic hepatocytes. [Fructose 2,6-bisphosphate] was also diminished in ischaemic liver, skeletal muscle and heart. 3. The following changes in metabolite concentration were observed in anaerobic hepatocytes: AMP, ADP, lactate and L-glycerol 3-phosphate were increased; ATP, citrate and pyruvate were decreased: phosphoenolpyruvate and hexose 6-phosphates were little affected. Concentrations of adenine nucleotides were, however, little changed by anoxia when hepatocytes from fed rats were incubated with 50 mM-glucose. 4. The activity of ATP:fructose 6-phosphate 2-phosphotransferase was not affected by anoxia but decreased by cyclic AMP. 5. The role of fructose 2,6-bisphosphate in the regulation of glycolysis is discussed.

Renotropic and gonadotropic activity in homologous and heterologous hybrids of ovine luteinizing hormone and human chorionic gonadotropin subunits

1991 ◽  
Vol 125 (6) ◽  
pp. 590-594 ◽  
Author(s):  
Kaoru Nomura ◽  
Yasunori Nakamura ◽  
Makoto Ujihara ◽  
Kazutaka Ohmura ◽  
Shohzou Toraya ◽  
...  
Keyword(s):  
Luteinizing Hormone ◽  
Cyclic Amp ◽  
Thymidine Incorporation ◽  
Special Role ◽  
Sulphate Group ◽  
Common Structure ◽  
Hypophysectomized Rats ◽  
Gonadotropic Activity ◽  
Stimulation Of

Abstract. We previously demonstrated the renotropic activity of ovine and porcine LH, i.e. the stimulation of [3H]thymidine incorporation into the renal DNA of castrated hypophysectomized rats. We conducted this study to determine which condition is required to promote renotropic activity. We prepared homologous (oLHα· oLHβ, hCGα·hCGβ) and heterologous (oLHα·hCGβ, hCGα·oLHβ) hybrids from isolated oLH- and/or hCG-derived subunits. Native oLH and all hybrids showed gonadotropic activity when examined for cyclic AMP generation in cultured Leydig tumour cells (MA-10). Native oLH and the hybrids which showed renotropic activity were all found to contain at least one of the oLH subunits. Our findings point out the important, special role of oLH subunits in promoting renotropic activity. The condition required is suggested to be presence of a common structure in the two oLH subunits. Such a structure should consequently not be present in hCG. A carbohydrate moiety of oLH containing a sulphate group is proposed as a candidate, but the assumption remains to be demonstrated.

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