scholarly journals Responsiveness to glucagon by isolated rat hepatocytes controlled by the redox state of the cytosolic nicotinamide—adenine dinucleotide couple acting on adenosine 3′:5′-cyclic monophosphate phosphodiesterase

1978 ◽  
Vol 176 (3) ◽  
pp. 805-816 ◽  
Author(s):  
M G Clark ◽  
I G Jarrett
Keyword(s):  
Cyclic Amp ◽  
Redox State ◽  
Rat Hepatocytes ◽  
Hormonal Control ◽  
Maximal Velocity ◽  
Isolated Rat Hepatocytes ◽  
Cyclic Amp Phosphodiesterase ◽  
Membrane Bound ◽  
Glucose Output ◽  
Isolated Rat

1. The effects of changes in the cytoplasmic [NADH]/[NAD+] ratio on the efficacy of glucagon to alter rates of metabolism in isolated rat hepatocytes were examined. 2. Under reduced conditions (with 10mM-lactate), 10nM-glucagon stimulated both gluconeogenesis and urea synthesis in isolated hepatocytes from 48h-starved rats; under oxidized conditions (with 10mM-pyruvate), 10nM-glucagon had no effect on either of these rates. 3. The ability of glucagon to alter the concentration of 3′:5′-cyclic AMP and the rates of glucose output, glycogen breakdown and glycolysis in cells from fed rats were each affected by a change in the extracellular [lactate]/[pyruvate] ratio; minimal effects of glucagon occurred at low [lactate]/[pyruvate] ratios. 4. Dose-response curves for glucagon-mediated changes in cyclic AMP concentration and glucose output indicated that under oxidized conditions the ability of glucagon to alter each parameter was decreased without affecting the concentration of hormone at which half-maximal effects occurred. 5. The phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (0.05 mM) significantly reversed the inhibitory effects of pyruvate on glucagon-stimulated glucose output. 6. For exogenously added cyclic [3H]AMP(0.1 mM), oxidized conditions decreased the stimulatory effect on glucose output as well as the intracellular concentration of cyclic AMP attained, but did not alter the amount of cyclic [3H]AMP taken up. 7. The effects of lactate, pyruvate, NAD+ and NADH on cyclic AMP phosphodiesterase activities of rat hepatocytes were examined. 8. NADH (0.01–1 MM) inhibited the low-Km enzyme, particularly that which was associated with the plasma membrane. 9. The inhibition of membrane-bound cyclic AMP phosphodiesterase by NADH was specific, reversible and resulted in a decrease in the maximal velocity of the enzyme. 10. It is proposed that regulation of the membrane-bound low-Km cyclic AMP phosphodiesterase by nicotinamide nucleotides provides the molecular basis for the effect of redox state on the hormonal control of hepatocyte metabolism by glucagon.

scholarly journals Calcium rather than cyclic AMP is an intracellular messenger of parathyroid hormone action on glycogen metabolism in isolated rat hepatocytes

1989 ◽  
Vol 258 (3) ◽  
pp. 889-894 ◽  
Author(s):  
T Mine ◽  
I Kojima ◽  
E Ogata
Keyword(s):  
Parathyroid Hormone ◽  
Cyclic Amp ◽  
Glucose Production ◽  
Rat Hepatocytes ◽  
Free Calcium ◽  
Dependent Manner ◽  
Isolated Rat Hepatocytes ◽  
Glucose Output ◽  
Dose Dependent ◽  
Isolated Rat

The synthetic 1-34 fragment of human parathyroid hormone (1-34hPTH) stimulated glucose production in isolated rat hepatocytes. The effect of 1-34hPTH was dose-dependent and 10(10) M-1-34 hPTH elicited the maximum glucose output, which was approx. 80% of that by glucagon. Although 1-34hPTH induced a small increase in cyclic AMP production at concentrations higher than 10(-9) M, 10(-10) M-1-34hPTH induced the maximum glucose output without significant elevation of cyclic AMP. This is in contrast to the action of forskolin, which increased glucose output to the same extent as 10(-10) M-1-34hPTH by causing a 2-fold elevation of cyclic AMP. In addition to increasing cyclic AMP, 1-34hPTH caused an increase in cytoplasmic free calcium concentration ([Ca2+]c). When the effect of 1-34hPTH on [Ca2+]c was studied in aequorin-loaded cells, low concentrations of 1-34hPTH increased [Ca2+]c: the 1-34hPTH effect on [Ca2+]c was detected at as low as 10(-12) M and increased in a dose-dependent manner. 1-34hPTH increased [Ca2+]c even in the presence of 1 microM extracellular calcium, suggesting that PTH mobilizes calcium from an intracellular pool. In line with these observations, 1-34hPTH increased the production of inositol trisphosphate. These results suggest that: (1) PTH activates both cyclic AMP and calcium messenger systems and (2) PTH stimulates glycogenolysis mainly via the calcium messenger system.

scholarly journals Glycogenolytic effect of pancreastatin in isolated rat hepatocytes is mediated by a cyclic-AMP-independent Ca2+-dependent mechanism

1992 ◽  
Vol 284 (3) ◽  
pp. 659-662 ◽  
Author(s):  
V Sánchez ◽  
M Lucas ◽  
J R Calvo ◽  
R Goberna
Keyword(s):  
Cyclic Amp ◽  
Lactate Production ◽  
Rat Hepatocytes ◽  
Isolated Rat Hepatocytes ◽  
Glycogenolytic Effect ◽  
Glucose Output ◽  
Camp Levels ◽  
Isolated Rat ◽  
Dependent Mechanism

We have studied the effect of pig pancreastatin on glucose and lactate production in freshly isolated rat hepatocytes. Pancreastatin stimulated the rate of glucose output, whereas, in contrast with glucagon, it failed to modify the rate of lactate production. The effective concentration of pancreastatin was in the range 0.1-100 nM, with half-maximal rate close to 1 nM. The ability of pancreastatin to increase glucose output was abolished by chelation of the calcium in the medium. By itself, pancreastatin did not increase cyclic AMP (cAMP) levels and had no influence on cAMP levels in glucagon-stimulated hepatocytes. Our results point out a possible role of pancreastatin in glycogenolysis. This appears to be mediated by a cAMP-independent Ca(2+)-dependent mechanism.

scholarly journals Hormonal control of fructose 2,6-bisphosphate concentration in isolated rat hepatocytes

1983 ◽  
Vol 214 (3) ◽  
pp. 829-837 ◽  
Author(s):  
R Bartrons ◽  
L Hue ◽  
E Van Schaftingen ◽  
H G Hers
Keyword(s):  
Cyclic Amp ◽  
Pyruvate Kinase ◽  
Time Course ◽  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Hormonal Control ◽  
Isolated Rat Hepatocytes ◽  
Free System ◽  
Significant Difference ◽  
Dependent Protein

The ability of glucagon and of adrenaline to affect the concentration of fructose 2,6-bisphosphate in isolated hepatocytes was re-investigated because of important discrepancies existing in the literature. We were unable to detect a significant difference in the sensitivity of the hepatocytes with regard to the effect of glucagon to initiate the interconversion of phosphorylase, pyruvate kinase, 6-phosphofructo-2-kinase and fructose 2,6-bisphosphatase, and also to cause the disappearance of fructose 2,6-bisphosphate. In contrast, we have observed differences in the time-course of these various changes, since the interconversions of phosphorylase and of pyruvate kinase were at least twice as fast as those of 6-phosphofructo-2-kinase and of fructose 2,6-bisphosphatase. When measured in a cell-free system in the presence of MgATP, the cyclic AMP-dependent interconversion of pyruvate kinase was 5-10-fold more rapid than those of 6-phosphofructo-2-kinase and of fructose 2,6-bisphosphatase. These data indicate that 6-phosphofructo-2-kinase and fructose 2,6-bisphosphatase are relatively poor substrates for cyclic AMP-dependent protein kinase; they also support the hypothesis that the two catalytic activities belong to a single protein. Adrenaline had only a slight effect on the several parameters under investigation, except for the activation of phosphorylase. In the absence of Ca2+ ions from the incubation medium, however, adrenaline had an effect similar to that of glucagon.

Effect of Somatomedin A and Insulin on Cyclic AMP Generation in Isolated Rat Hepatocytes

1980 ◽  
Vol 12 (06) ◽  
pp. 251-256 ◽  
Author(s):  
Rosa Zederman ◽  
Carin Grebing ◽  
Kerstin Hall ◽  
H. Löw
Keyword(s):  
Cyclic Amp ◽  
Rat Hepatocytes ◽  
Isolated Rat Hepatocytes ◽  
Isolated Rat

scholarly journals Stimulatory effect of the intestinal peptide PHI on glycogenolysis and gluconeogenesis in isolated rat hepatocytes

1983 ◽  
Vol 214 (3) ◽  
pp. 999-1002 ◽  
Author(s):  
J E Felíu ◽  
J Marco
Keyword(s):  
Cyclic Amp ◽  
Pyruvate Kinase ◽  
Glycogen Phosphorylase ◽  
Rat Hepatocytes ◽  
Fold Increase ◽  
Isolated Rat Hepatocytes ◽  
Mediated Effects ◽  
Dose Dependent ◽  
Isolated Rat ◽  
Stimulation Of

The newly isolated peptide PHI provoked a dose-dependent stimulation of glycogenolysis and gluconeogenesis in isolated rat hepatocytes; at 1 microM-PHI, both processes were increased 1.6-fold as compared with basal values. These PHI-mediated effects were accompanied by the activation of glycogen phosphorylase and the inactivation of pyruvate kinase. PHI (1 microM) also caused a 2-fold increase in hepatocyte cyclic AMP.

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