scholarly journals Effect of glucagon on metabolite compartmentation in isolated rat liver cells during gluconeogenesis from lactate

1977 ◽  
Vol 166 (2) ◽  
pp. 225-235 ◽  
Author(s):  
Elmar A. Siess ◽  
Dietrich G. Brocks ◽  
Herbert K. Lattke ◽  
Otto H. Wieland
Keyword(s):  
Adenine Nucleotides ◽  
Isolated Hepatocytes ◽  
Cell Fractionation ◽  
Acetyl Coa ◽  
Isolated Rat Liver ◽  
Rat Liver Cells ◽  
The Matrix ◽  
Isolated Rat ◽  
Reduced State ◽  
Stimulation Of

1. The subcellular distribution of adenine nucleotides, acetyl-CoA, CoA, glutamate, 2-oxoglutarate, malate, oxaloacetate, pyruvate, phosphoenolpyruvate, 3-phosphoglycerate, glucose 6-phosphate, aspartate and citrate was studied in isolated hepatocytes in the absence and presence of glucagon by using a modified digitonin procedure for cell fractionation. 2. In the absence of glucagon, the cytosol contains about two-thirds of cellular ATP, some 40–50% of ADP, acetyl-CoA, citrate and phosphoenolpyruvate, more than 75% of total 2-oxoglutarate, glutamate, malate, oxaloacetate, pyruvate, 3-phosphoglycerate and aspartate, and all of glucose 6-phosphate. 3. In the presence of glucagon the cytosolic space shows an increase in the content of malate, phosphoenolpyruvate and 3-phosphoglycerate by more than 60%, and those of aspartate and glucose 6-phosphate rise by about 25%. Other metabolites remain unchanged. After glucagon treatment, cytosolic pyruvate is decreased by 37%, whereas glutamate and 2-oxoglutarate decrease by 70%. The [NAD+]/[NADH] ratios calculated from the cytosolic concentrations of the reactants of lactate dehydrogenase and malate dehydrogenase were the same. Glucagon shifts this ratio and also that of the [NADP+]/[NADPH] couple towards a more reduced state. 4. In the mitochondrial space glucagon causes an increase in the acetyl-CoA and ATP contents by 25%, and an increase in [phosphoenolpyruvate] by 50%. Other metabolites are not changed by glucagon. Oxaloacetate in the matrix is only slightly decreased after glucagon, yet glutamate and 2-oxoglutarate fall to about 25% of the respective control values. The [NAD+]/[NADH] ratios as calculated from the [3-hydroxybutyrate]/[acetoacetate] ratio and from the matrix [malate]/[oxaloacetate] couple are lowered by glucagon, yet in the latter case the values are about tenfold higher than in the former. 5. Glucagon and oleate stimulate gluconeogenesis from lactate to nearly the same extent. Oleate, however, does not produce the changes in cellular 2-oxoglutarate and glutamate as observed with glucagon. 6. The changes of the subcellular metabolite distribution after glucagon are compatible with the proposal that the stimulation of gluconeogenesis results from as yet unknown action(s) of the hormone at the mitochondrial level in concert with its established effects on proteolysis and lipolysis.

Glycerol-induced adenine nucleotide catabolism in rat liver cells

1982 ◽  
Vol 60 (12) ◽  
pp. 1101-1108 ◽  
Author(s):  
Christine Des Rosiers ◽  
Marcel Lalanne ◽  
Joan Willemot
Keyword(s):  
Rat Liver ◽  
Adenine Nucleotide ◽  
Adenine Nucleotides ◽  
Liver Cells ◽  
Transient Increase ◽  
Isolated Rat Liver ◽  
Rat Liver Cells ◽  
Isolated Rat

Prelabeled adenine nucleotides were rapidly degraded in freshly isolated rat liver cells incubated with glycerol at concentrations greater than 0.25 mM. Concomitantly, the [14C]ATP/[14C]ADP and [14C]ATP/[14C]AMP ratios were decreased. There was a transient increase in radioactive IMP, inosine, and hypoxanthine and a constant accumulation of allantoin. Radioactive adenosine also accumulated transiently under certain conditions. The intracellular Pi; concentration was decreased. The magnitude of most of these changes was dependent upon the concentration of glycerol. The effects of glycerol were similar to those of fructose. The extent of endogenous adenine nucleotide catabolism was smaller at high Pi concentration, whereas the extent of glycerol-induced catabolism was unaffected. However, less inosine and more hypoxanthine accumulated during glycerol-induced catabolism at high Pi concentration.

scholarly journals Glucagon and vasopressin interactions on Ca2+ movements in isolated hepatocytes

1986 ◽  
Vol 237 (3) ◽  
pp. 675-683 ◽  
Author(s):  
L Combettes ◽  
B Berthon ◽  
A Binet ◽  
M Claret
Keyword(s):  
Endoplasmic Reticulum ◽  
Rat Liver ◽  
Isolated Hepatocytes ◽  
Liver Cells ◽  
Isolated Rat Liver ◽  
Low Concentration ◽  
Fast Phase ◽  
Rat Liver Cells ◽  
Subsequent Addition ◽  
Isolated Rat

The effects of glucagon and vasopressin, singly or together, on cytosolic free Ca2+ concentration [(Ca2+]i) and on the 45Ca2+ efflux were studied in isolated rat liver cells. In the presence of 1 mM external Ca2+, glucagon and vasopressin added singly induced sustained increases in [Ca2+]i. The rate of the initial fast phase of the [Ca2+]i increase and the magnitude of the final plateau were dependent on the concentrations (50 pm-0.1 microM) of glucagon and vasopressin. Preincubating the cells with a low concentration of glucagon (0.1 nM) for 2 min markedly accelerated the fast phase and elevated the plateau of the [Ca2+]i increase caused by vasopressin. In the absence of external free Ca2+, glucagon and vasopressin transiently increased [Ca2+]i and stimulated the 45Ca2+ efflux from the cells, indicating mobilization of Ca2+ from internal store(s). Preincubating the cells with 0.1 nM-glucagon accelerated the rate of the fast phase of the [Ca2+]i rise caused by the subsequent addition of vasopressin. However, unlike what was observed in the presence of 1 mM-Ca2+, glucagon no longer enhanced the maximal [Ca2+]i response to vasopressin. In the absence of external free Ca2+, higher concentrations (1 nM-0.1 microM) of glucagon, which initiated larger increases in [Ca2+]i, drastically decreased the subsequent Ca2+ response to vasopressin (10 nM). At these concentrations, glucagon also decreased the vasopressin-stimulated 45Ca2+ efflux from the cells. It is suggested that, in the liver, glucagon accelerates the fast phase and elevates the plateau of the vasopressin-mediated [Ca2+]i increase respectively by releasing Ca2+ from the same internal store as that permeabilized by vasopressin, probably the endoplasmic reticulum, and potentiating the influx of extracellular Ca2+ caused by this hormone.

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