scholarly journals Regulation of mitochondrial pyruvate carboxylation in isolated hepatocytes by acute insulin treatment

1983 ◽  
Vol 214 (2) ◽  
pp. 451-458 ◽  
Author(s):  
A B Chisholm ◽  
E H Allan ◽  
M A Titheradge
Keyword(s):  
Insulin Treatment ◽  
Second Messengers ◽  
Isolated Hepatocytes ◽  
Carboxylase Activity ◽  
Effector Molecules ◽  
Pyruvate Carboxylation ◽  
Isolated Mitochondria ◽  
Glucose Synthesis ◽  
Important Site ◽  
Stimulation Of

The effect of acute insulin treatment of hepatocytes on pyruvate carboxylation in both isolated mitochondria and cells rendered permeable by filipin was examined. Challenging the cells with insulin alone had no effect on either the basal rate of pyruvate carboxylation or gluconeogenesis, although it did suppress the responses to both glucagon and catecholamines. Insulin treatment was unable to antagonize the enhanced rate of pyruvate carboxylation caused by stimulation of the cells with either angiotensin or vasopressin. Neither insulin nor the gluconeogenic hormones altered the total extractable pyruvate carboxylase activity in the isolated mitochondria, suggesting that the effect of hormones at the level of the isolated intact organelle was mediated via alterations in the intramitochondrial concentrations of effector molecules, notably ATP and the [ATP]/[ADP] ratio and substrate availability. The alterations in pyruvate carboxylation correlate well with glucose synthesis in terms of sensitivity to effector molecules, putative second messengers and time of onset of the response, indicating that alterations in the flux through this enzyme are compatible with it being an important site in the control of gluconeogenesis from C3 precursors.

scholarly journals Lactate-stimulated ethanol oxidation in isolated hepatocytes

1978 ◽  
Vol 172 (1) ◽  
pp. 29-36 ◽  
Author(s):  
Kathryn E. Crow ◽  
Neal W. Cornell ◽  
Richard L. Veech
Keyword(s):  
Ethanol Oxidation ◽  
Lactate Concentration ◽  
Isolated Hepatocytes ◽  
Cell Preparation ◽  
O2 Uptake ◽  
Glucose Synthesis ◽  
The Relationship ◽  
Pyruvate Ratio ◽  
Stimulation Of

1. Hepatocytes isolated from starved rats and incubated without other substrates oxidized ethanol at a rate of 0.8–0.9μmol/min per g wet wt. of cells. Addition of 10mm-lactate increased this rate 2-fold. 2. Quinolinate (5mm) or tryptophan (1mm) decreased the rate of gluconeogenesis with 10mm-lactate and 8mm-ethanol from 0.39 to 0.04–0.08μmol/min per g wet wt. of cells, but rates of ethanol oxidation were not decreased. From these results it appears that acceleration of ethanol oxidation by lactate is not dependent upon the stimulation of gluconeogenesis and the consequent increased demand for ATP. 3. As another test of the relationship between ethanol oxidation and gluconeogenesis, the initial lactate concentration was varied from 0.5mm to 10mm and pyruvate was added to give an initial [lactate]/[pyruvate] ratio of 10. This substrate combination gave a large stimulation of ethanol oxidation (from 0.8 to 2.6μmol/min per g wet wt. of cells) at low lactate concentrations (0.5–2.0mm), but rates remained nearly constant (2.6–3.0μmol/min per g wet wt. of cells) at higher lactate concentrations (2.0–10mm). 4. In contrast, owing to the presence of ethanol, the rate of glucose synthesis was only slightly increased (from 0.08 to 0.12μmol/min per g wet wt. of cells) between 0.5mm- and 2.0mm-lactate and continued to increase (from 0.12 to 0.65μmol/min per g wet wt. of cells) with lactate concentrations between 2 and 10mm. 5. In the presence of ethanol, O2 uptake increased with increasing substrate concentration over the entire range. 6. Changes in concentrations of glutamate and 2-oxoglutarate closely paralleled changes in the rate of ethanol oxidation. 7. In isolated hepatocytes, rates of ethanol oxidation are lower than those in vivo apparently because of depletion of malate–aspartate shuttle intermediates during cell preparation. Rates are returned to those observed in vivo by substrates that increase the intracellular concentration of shuttle metabolites.

scholarly journals Hormonal stimulation of mitochondrial pyruvate carboxylation in filipin-treated hepatocytes

1983 ◽  
Vol 212 (2) ◽  
pp. 417-426 ◽  
Author(s):  
E H Allan ◽  
A B Chisholm ◽  
M A Titheradge
Keyword(s):  
Phosphoenolpyruvate Carboxykinase ◽  
Co2 Fixation ◽  
Hormone Action ◽  
Acute Effects ◽  
Polyene Antibiotic ◽  
Hormonal Stimulation ◽  
Pyruvate Carboxylation ◽  
Isolated Mitochondria ◽  
Stimulation Of

A method is described for measuring rates of mitochondrial pyruvate carboxylation in hepatocytes treated with the polyene antibiotic, filipin, to render the plasma membrane permeable to substrates. With this approach it was possible to demonstrate that treatment of cells with glucagon or catecholamines results in a stimulation of mitochondrial CO2 fixation measured in situ comparable with that observed in the isolated mitochondria, in terms of time of onset of the response, hormone selectivity and sensitivity. In addition, angiotensin II and vasopressin were shown to enhance the activity of pyruvate carboxylase in both the intact mitochondria and filipin-treated cells, thus strengthening the postulate that this site is a major locus of hormone action in the control of gluconeogenesis. Addition of 3-mercaptopicolinic acid, to inhibit gluconeogenesis at the level of phosphoenolpyruvate carboxykinase, had no significant effect on the stimulation of pyruvate carboxylation by adrenaline, suggesting that the effect of the hormone at this site is independent of changes in activity of other enzymes further on in the pathway. The data presented preclude the possibility that acute effects of hormones on mitochondrial metabolism are solely artifacts of the preparation procedure.

Sensory Transduction

2019 ◽  
Author(s):  
Gordon L. Fain
Keyword(s):  
Ion Channels ◽  
Receptor Cell ◽  
Electrical Response ◽  
Second Messengers ◽  
Sensory Transduction ◽  
Sensory Receptor ◽  
Signal Pathways ◽  
Sense Organs ◽  
Sensory Physiology ◽  
Effector Molecules

Sensory Transduction provides a thorough and easily accessible introduction to the mechanisms that each of the different kinds of sensory receptor cell uses to convert a sensory stimulus into an electrical response. Beginning with an introduction to methods of experimentation, sensory specializations, ion channels, and G-protein cascades, it provides up-to-date reviews of all of the major senses, including touch, hearing, olfaction, taste, photoreception, and the “extra” senses of thermoreception, electroreception, and magnetoreception. By bringing mechanisms of all of the senses together into a coherent treatment, it facilitates comparison of ion channels, metabotropic effector molecules, second messengers, and other components of signal pathways that are common themes in the physiology of the different sense organs. With its many clear illustrations and easily assimilated exposition, it provides an ideal introduction to current research for the professional in neuroscience, as well as a text for an advanced undergraduate or graduate-level course on sensory physiology.

scholarly journals Rapid and delayed effects of epidermal growth factor on gluconeogenesis

1993 ◽  
Vol 294 (3) ◽  
pp. 865-872 ◽  
Author(s):  
C Soler ◽  
M Soley
Keyword(s):  
Growth Factor ◽  
Epidermal Growth Factor ◽  
Redox State ◽  
Metabolic Flux ◽  
Isolated Hepatocytes ◽  
Delayed Effect ◽  
Delayed Effects ◽  
Mitochondrial Redox State ◽  
Glucose Synthesis ◽  
Epidermal Growth

Most reports on the effects of epidermal growth factor (EGF) on gluconeogenesis have indicated that such effects depend on the substrate used and are only observable after a lag time of 30-40 min. Recently, an immediate and transient effect of EGF on glucose synthesis was described in a perfused liver system. Here we extend the study of the effect of EGF on gluconeogenesis to isolated hepatocytes from fasted rats. The delayed effect of EGF on gluconeogenesis was studied by adding the substrate 40 min after the peptide. Under these conditions EGF increased glucose synthesis from pyruvate, decreased it when the substrate was lactate or glycerol and did not modify gluconeogensis from fructose or dihydroxyacetone. EGF did not affect the metabolic flux through glycolysis, determined as the production of lactate+pyruvate from 30 mM glucose. Furthermore, EGF did not modify the metabolic flux through pyruvate kinase, determined as the production of lactate+pyruvate from 1 mM dihydroxyacetone. The differing effects of EGF on gluconeogenesis depending on the substrate used can be explained by the effects of EGF on the cytosolic redox state (measured as the lactate/pyruvate ratio). About 20 min after the addition of EGF, the mitochondrial redox state (measured as the 3-hydroxybutyrate/acetoacetate ratio) decreased. This effect of EGF was blocked by ammonium, which also abolished the effect of the peptide on gluconeogenesis. Thus the effect of EGF at the mitochondrial level appears to be necessary for its effects on gluconeogenesis. Taken together, our results indicate that the delayed effects of EGF on gluconeogenesis are secondary to the effects of the peptide at both the mitochondrial and cytosolic levels. In addition to these delayed effects, we observed that EGF rapidly and transiently stimulated glucose synthesis from lactate, decreased the cytosolic redox state and increased oxygen consumption. All of these rapid effects required the presence of extracellular calcium and disappeared in the presence of rotenone, suggesting that this rapid effect of EGF on gluconeogenesis is secondary to the stimulation of mitochondrial respiration.

scholarly journals Natural polyamines stimulate G-proteins

1992 ◽  
Vol 282 (2) ◽  
pp. 545-550 ◽  
Author(s):  
J L Bueb ◽  
A Da Silva ◽  
M Mousli ◽  
Y Landry
Keyword(s):  
Mast Cells ◽  
Pertussis Toxin ◽  
Inositol Phosphates ◽  
Second Messengers ◽  
G Protein Coupled Receptors ◽  
Extracellular Signals ◽  
Physiological Relevance ◽  
G Protein Coupled ◽  
Stimulation Of ◽  
Rat Mast Cells

The natural polyamines spermine and spermidine, the biosynthetic precursor putrescine and their analogues cadaverine and tyramine stimulate the GTPase activity of purified GTP-binding proteins (Go/Gi) from calf brain reconstituted into phospholipid vesicles. The order of potency was spermine greater than spermidine greater than putrescine = cadaverine greater than tyramine. The physiological relevance of this observation was assessed, showing the same order of potency of polyamines in the stimulation of peritoneal and tracheal rat mast cells. The activation of rat mast cells by polyamines was inhibited by benzalkonium chloride or by a 2 h pretreatment of the cells with pertussis toxin. The increase in inositol phosphates evoked by polyamines was also inhibited by pertussis toxin. Therefore we propose that intracellular polyamines might control the basal level of second messengers and modulate extracellular signals transduced through G-protein-coupled receptors.

scholarly journals Stimulation of interleukin-6 production by endothelin in rat bone marrow-derived stromal cells

Blood ◽  
1994 ◽  
Vol 84 (8) ◽  
pp. 2531-2538 ◽  
Author(s):  
T Agui ◽  
X Xin ◽  
Y Cai ◽  
T Sakai ◽  
K Matsumoto
Keyword(s):  
Bone Marrow ◽  
Stromal Cells ◽  
Interleukin 6 ◽  
Hormonal Regulation ◽  
Ex Vivo ◽  
Second Messengers ◽  
Immunodeficiency Virus ◽  
Rat Bone ◽  
Stimulation Of

Abstract Endothelin (ET) produced by endothelial cells has recently been found to be a potent vasoconstricting hormone. In this report, ET is shown to be a potent stimulator of interleukin-6 (IL-6) production by rat bone marrow (BM)-derived stromal cells. It was also shown that ET increased the level of mRNA for IL-6 in these cells. The two types of ET receptor (R), ETAR and ETBR, were shown to be expressed on both BM-derived stromal cells in culture and ex vivo in BM tissue, suggesting that ET works as a physiologic stimulator of IL-6 production in the BM. It was shown that ETAR is coupled to phospholipase C activation, leading to the production of inositol 1,4,5-trisphosphate (IP3) and 1,2- diacylglycerol (DAG) as second messengers in BM-derived stromal cells. This was corroborated by data showing that IL-6 production in these cells was induced by combined stimulation with ionomycin and phorbol myristate acetate, thereby bypassing the effects of IP3 and DAG, respectively. This is the first report on the hormonal regulation of IL- 6 production by BM stromal cells, indicating that hematopoiesis is subject to endocrinologic regulation under physiologic conditions. ET has recently been reported to be produced by macrophages in response to bacterial lipopolysaccharide and human immunodeficiency virus-1 glycoprotein 120. These facts, taken together with our findings, raise the possibility that ET shares the same role of IL-1 as a local cytokine, mediating an intercellular signal between macrophages and BM stromal cells in response to bacterial or viral stimulation.

scholarly journals Insulin-independent, MAPK-dependent stimulation of NKCC activity in skeletal muscle

2001 ◽  
Vol 281 (2) ◽  
pp. R561-R571 ◽  
Author(s):  
Jennifer A. Wong ◽  
Aidar R. Gosmanov ◽  
Edward G. Schneider ◽  
Donald B. Thomason
Keyword(s):  
Skeletal Muscle ◽  
Atpase Activity ◽  
Insulin Treatment ◽  
Ex Vivo ◽  
Mitogen Activated Protein Kinase ◽  
Extracellular Signal Regulated Kinase ◽  
Extracellular Signal ◽  
Mitogen Activated Protein ◽  
Significant Pathway ◽  
Stimulation Of

Na+-K+-Cl−cotransporter (NKCC) activity in quiescent skeletal muscle is modest. However, ex vivo stimulation of muscle for as little as 18 contractions (1 min, 0.3 Hz) dramatically increased the activity of the cotransporter, measured as the bumetanide-sensitive 86Rb influx, in both soleus and plantaris muscles. This activation of cotransporter activity remained relatively constant for up to 10-Hz stimulation for 1 min, falling off at higher frequencies (30-Hz stimulation for 1 min). Similarly, stimulation of skeletal muscle with adrenergic receptor agonists phenylephrine, isoproterenol, or epinephrine produced a dramatic stimulation of NKCC activity. It did not appear that stimulation of NKCC activity was a reflection of increased Na+-K+-ATPase activity because insulin treatment did not stimulate NKCC activity, despite insulin's well-known stimulation of Na+-K+-ATPase activity. Stimulation of NKCC activity could be blocked by pretreatment with inhibitors of mitogen-activated protein kinase (MAPK) kinase 1/2 (MEK1/2) activity, indicating that activation of the extracellular signal-regulated kinase 1/2 (ERK1/2) MAPKs may be required. These data indicate a regulated NKCC activity in skeletal muscle that may provide a significant pathway for potassium transport into skeletal muscle fibers.

Sign in / Sign up

Export Citation Format

Share Document