scholarly journals Stimulation of hepatic inositol 1,4,5-trisphosphate kinase activity by Ca2+-dependent and -independent mechanisms

1988 ◽  
Vol 256 (3) ◽  
pp. 697-701 ◽  
Author(s):  
T J Biden ◽  
J G Altin ◽  
A Karjalainen ◽  
F L Bygrave
Keyword(s):  
Cyclic Amp ◽  
Kinase Activity ◽  
Rat Hepatocytes ◽  
Cytosolic Fraction ◽  
Dibutyryl Cyclic Amp ◽  
Assay Medium ◽  
Tetradecanoylphorbol Acetate ◽  
Inositol 1,4,5 Trisphosphate ◽  
Stimulation Of

A cytosolic fraction derived from rat hepatocytes was used to investigate the regulation of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] kinase, the enzyme which converts Ins(1,4,5)P3 to inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P4]. The activity was doubled by raising the free Ca2+ concentration of the assay medium from 0.1 microM to 1.0 microM. A 5 min preincubation of the hepatocytes with 100 microM-dibutyryl cyclic AMP (db.cAMP) plus 100 nM-tetradecanoylphorbol acetate (TPA) resulted in a 40% increase in Ins(1,4,5)P3 kinase activity when subsequently assayed at 0.1 microM-Ca2+. This effect was smaller at [Ca2+] greater than 0.5 microM, and absent at 1.0 microM-Ca2+. Similar results were obtained after preincubation with 100 microM-db.cAMP plus 300 nM-vasopressin (20% increase at 0.1 microM-Ca2+; no effect at 1.0 microM-Ca2+). Preincubation with vasopressin, db.cAMP or TPA alone did not alter Ins(1,4,5)P3 kinase activity. It is proposed that these results, together with recent evidence implicating Ins(1,3,4,5)P4 in the control of Ca2+ influx, could be relevant to earlier findings that hepatic Ca2+ uptake is synergistically stimulated by cyclic AMP analogues and vasopressin.

scholarly journals Stimulation by glucocorticoids of protein degradation in hepatocyte monolayers

1981 ◽  
Vol 196 (1) ◽  
pp. 33-40 ◽  
Author(s):  
M F Hopgood ◽  
M G Clark ◽  
F J Ballard
Keyword(s):  
Cyclic Amp ◽  
Protein Degradation ◽  
Monolayer Culture ◽  
Rat Hepatocytes ◽  
Protein Breakdown ◽  
Dibutyryl Cyclic Amp ◽  
Intracellular Proteins ◽  
Autophagic Process ◽  
Soluble Material ◽  
Stimulation Of

1. Protein degradation in rat hepatocytes in stationary monolayer culture was measured as release of radioactive trichloroacetic acid-soluble material from intracellular proteins labelled with [3H]leucine. 2. Glucocorticoids, but not other steroids, stimulated protein breakdown in the hepatocyte monolayers. The effects observed were greater when the cells were preincubated with the hormones, indicating that the stimulation was not immediate. In addition, the stimulation by glucocorticoids persisted for up to 4 h after hormone removal. 3. Cycloheximide and the lysosomotropic agents leupeptin and ammonia effectively blocked glucocorticoid stimulation of protein degradation. 4. Insulin blocked dexamethasone stimulation when added at the same time as the steroid, but not when added 3 h later. 5. Stimulation of protein breakdown by dexamethasone was additive with that by glucagon or dibutyryl cyclic AMP, suggesting that its mechanism of action is different from that of the latter two agents. 6. Total activities of several lysosomal enzymes were unaffected under conditions where protein breakdown was stimulated by either glucagon or dexamethasone. 7. It is suggested that, whereas glucagon, dibutyryl cyclic AMP and insulin modulate protein breakdown in these cells via changes in autophagocytosis, the stimulation by glucocorticoids is exerted independently, perhaps by stimulating the synthesis of membrane proteins essential to the autophagic process.

scholarly journals Evidence that stimulation of plasma-membrane Ca2+ inflow is an early action of glucagon and dibutyryl cyclic AMP in rat hepatocytes

1993 ◽  
Vol 292 (1) ◽  
pp. 19-22 ◽  
Author(s):  
F L Bygrave ◽  
A Gamberucci ◽  
R Fulceri ◽  
A Benedetti
Keyword(s):  
Plasma Membrane ◽  
Cyclic Amp ◽  
Rat Hepatocytes ◽  
Fixed Time ◽  
Time Interval ◽  
Dibutyryl Cyclic Amp ◽  
Fixed Time Interval ◽  
Early Action ◽  
Co Addition ◽  
Stimulation Of

The ability of glucagon (1 nM) and of dibutyryl cyclic AMP (50 microM) to increase cytosolic free Ca2+ concentration ([Ca2+]i) in Fura-loaded rat hepatocytes was examined in a system wherein Ca2+ inflow was induced by the re-admission of excess Ca2+ to a nominally Ca(2+)-free medium. An increase in [Ca2+]i did not occur in the absence of either agonist, but did so after co-addition of either agonist with Ca2+. Increasing the time between addition of dibutyryl cyclic AMP (or of glucagon) and Ca2+ led to increases in [Ca2+]i; half-maximal and maximal increases were observed at 0 s (i.e. at co-addition) and 5-7 s respectively. Dibutyryl cyclic AMP and Ca2+ each exhibited a concentration-dependence when their respective concentrations were changed for a fixed time interval between additions. Half-maximal and maximal effects were obtained with 30 microM and 50 microM dibutyryl cyclic AMP and with 0.5 mM and approx. 1 mM Ca2+ respectively. The data demonstrate an early action of glucagon and dibutyryl cyclic AMP on [Ca2+]i. It is argued that the agonist-induced rise in [Ca2+]i results from an increase in plasma-membrane Ca2+ inflow, an effect that appears to occur much earlier than that on mobilization of internal stores of Ca2+.

Inositol 1,4,5-trisphosphate 3-kinase activity in FRTL-5 cells: regulation of the enzyme activity by TSH

1995 ◽  
Vol 144 (3) ◽  
pp. 527-532 ◽  
Author(s):  
K Takazawa ◽  
M Go ◽  
T Endo ◽  
C Erneux ◽  
T Onaya
Keyword(s):  
Enzyme Activity ◽  
Cyclic Amp ◽  
Gel Electrophoresis ◽  
Kinase Activity ◽  
Polyacrylamide Gel Electrophoresis ◽  
Inhibitory Effect ◽  
Dibutyryl Cyclic Amp ◽  
Physiological Concentration ◽  
Thyroid Cells ◽  
Inositol 1,4,5 Trisphosphate

Abstract Inositol 1,4,5-trisphosphate (InsP3) 3-kinase phosphorylates the Ca2+-mobilizing second messenger InsP3 to inositol 1,3,4,5-tetrakisphosphate (InsP4). InsP3 5-phosphatase dephosphorylates InsP3 to inositol 1,4-bisphosphate (InsP2). We compared the effects of TSH added to a culture of FRTL-5 thyroid cells on the activity of InsP3 5-phosphatase and InsP3 3-kinase. InsP3 3-kinase activity was decreased at a physiological concentration of TSH. Inhibition of this activity started after 3 h of incubation with TSH and was maximal after 24 h. In contrast, InsP3 5-phosphatase activity was not affected by TSH under the same conditions. The inhibitory effect of TSH on InsP3 3-kinase was characterized as follows: a) inhibition of activity was mimicked by both dibutyryl cyclic AMP and forskolin; b) activity obtained by mixing lysates of TSH-stimulated and non-stimulated cells was the sum of each activity measured separately; c) inhibition persisted after a crude lysate of TSH-stimulated cells had been subjected to SDS/polyacrylamide gel electrophoresis and the extraction of InsP3 3-kinase activity. The data suggest that TSH reduced the activity of InsP3 3-kinase in FRTL-5 cells either by a phosphorylation/dephosphorylation mechanism, or by affecting expression of the enzyme. Journal of Endocrinology (1995) 144, 527–532

Control of brown adipose tissue lipolysis and respiration by adenosine

1983 ◽  
Vol 245 (6) ◽  
pp. E555-E559 ◽  
Author(s):  
D. Szillat ◽  
L. J. Bukowiecki
Keyword(s):  
Adipose Tissue ◽  
Cyclic Amp ◽  
Palmitic Acid ◽  
Brown Adipose Tissue ◽  
Brown Adipocyte ◽  
Tissue Respiration ◽  
Dibutyryl Cyclic Amp ◽  
Response Curves ◽  
Brown Adipose ◽  
Stimulation Of

Adenosine competitively inhibited the stimulatory effects of (-)-isoproterenol on lipolysis and respiration in hamster brown adipocytes. The low value of the apparent ki for respiratory inhibition by adenosine (7 nM) indicated that the nucleoside may control brown adipocyte function under physiological concentrations. Significantly, the dose-response curves for isoproterenol stimulation of lipolysis and respiration were both shifted by adenosine to higher agonist concentrations by the same order of magnitude, providing additional evidence for a tight coupling between lipolysis and respiration. The inhibitory effects of adenosine were rapidly reversed by a) adenosine deaminase, b) agents known to increase intracellular cyclic AMP levels (isoproterenol, isobutylmethylxanthine, dibutyryl cyclic AMP), and c) direct stimulation of respiration with palmitic acid. These results, combined with the fact that adenosine failed to affect respiration evoked either by dibutyryl cyclic AMP or by palmitic acid, strongly indicate that adenosine regulates brown adipose tissue respiration at an early metabolic step of the stimulus-thermogenesis sequence, most probably at the level of the adenylate cyclase complex.

Evidence for glomerular actions of ADH and dibutyryl cyclic AMP in the rat

1977 ◽  
Vol 233 (2) ◽  
pp. F102-F117
Author(s):  
I. Ichikawa ◽  
B. M. Brenner
Keyword(s):  
Cyclic Amp ◽  
Arginine Vasopressin ◽  
Urine Flow ◽  
Hydraulic Pressure ◽  
Dibutyryl Cyclic Amp ◽  
Water Diuresis ◽  
Single Nephron ◽  
Arterial Hemorrhage ◽  
Glomerular Ultrafiltration ◽  
Stimulation Of

Experiments were performed on 54 chronically water diuretic Munich-Wistar rats to investigate the effects of various antidiuretic peptides on the determinants of glomerular ultrafiltration. Transition from water diuresis to antidiuresis, induced either by intravenous infusion of 1) exogenous peptides (Pitressin, synthetic arginine vasopressin, or synthetic [1-deamino,4-valine]-8-D-arginine vasopressin) or 2) dibutyryl cyclic AMP, or by stimulation of endogenous ADH release by acute, mild arterial hemorrhage, was associated with near-constant or decreased values for single nephron (SN) and total kidney GFR. Nevertheless, the glomerular transcapillary hydraulic pressure difference (deltaP) uniformly increased with antidiuresis, due to consistent reductions in Bowman's space hydraulic pressure rather than to increases in glomerular capillary hydraulic pressure, the former a consequence of the fall in urine flow rate. In all antidiuretic states, the rats were uniformly observed to be at filtration pressure disequilibrium, permitting calculation of unique values of the glomerular ultrafiltration coefficient (Kf). These values of Kf in antidiuresis were invariably lower than the values obtained during water diuresis. Whether these effects of ADH and DBcAMP on deltaP and Kf represent physiological influences in the control of GFR remains uncertain; their offsetting effects in the present studies usually failed to alter GFR appreciably.

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