scholarly journals Phorbol-ester-induced alterations of free calcium ion transients in single rat hepatocytes

1987 ◽  
Vol 246 (3) ◽  
pp. 619-623 ◽  
Author(s):  
N M Woods ◽  
K S R Cuthbertson ◽  
P H Cobbold
Keyword(s):  
Phorbol Ester ◽  
Calcium Ion ◽  
Phorbol Esters ◽  
Rat Hepatocytes ◽  
Inhibitory Effect ◽  
Induced Response ◽  
Free Calcium

The effect of the phorbol esters phorbol 12-myristate 13-acetate (TPA) and phorbol 12,13-dibutyrate (PDB) on changes in free Ca2+ concentration ([Ca2+]i) in single rat hepatocytes, microinjected with the photoprotein aequorin, were investigated. [Arg8]vasopressin and phenylephrine induced a series of repetitive [Ca2+]i transients. Phorbol esters inhibited the alpha 1-adrenoceptor-induced response; sub-nanomolar concentrations decreased the transient frequency, and higher concentrations abolished the transients. The inhibitory effect of PDB was readily reversible. Phorbol esters were less effective in decreasing the frequency of [Arg8]-vasopressin-induced transients, and the inhibition could be overcome by high [Arg8]vasopressin concentrations.

scholarly journals Taurolithocholate-induced Ca2+ release is inhibited by phorbol esters in isolated hepatocytes

1992 ◽  
Vol 287 (3) ◽  
pp. 891-896 ◽  
Author(s):  
L Combettes ◽  
B Berthon ◽  
M Claret
Keyword(s):  
Bile Acid ◽  
Bile Acids ◽  
Phorbol Ester ◽  
Phorbol Esters ◽  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Inhibitory Effect ◽  
Cell Uptake ◽  
Intracellular Binding ◽  
Pkc Activation

The monohydroxy bile acid taurolithocholate (TLC) causes a rapid and transient increase in free cytosolic Ca2+ concentration ([Ca2+]i) in suspensions of rat hepatocytes similar to that elicited by the InsP3-dependent hormone vasopressin. The effect of the bile acid is due to a mobilization of Ca2+, independent of InsP3, from the endoplasmic reticulum (ER). Short-term preincubation of cells with the phorbol ester 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA), which activates protein kinase C (PKC), blocked the increase in [Ca2+]i induced by TLC, but did not alter that mediated by vasopressin. We obtained the following results, indicating that the effect of PMA is mediated by the activation of PKC. (1) Phorbol esters were effective over a concentration range where they activate PKC (IC50 = 0.5 nM); (2) phorbol esters that do not activate PKC did not inhibit the effects of TLC; (3) the permeant analogue oleoylacetylglycerol mimicked the inhibitory effect of PMA; (4) lastly, the inhibition of the TLC-induced Ca2+ mobilization by phorbol esters was partially prevented by preincubating the cells with the PKC inhibitors H7 and AMG-C16. Preincubating hepatocytes with PMA had no effect on the cell uptake of labelled TLC, indicating that the phorbol ester does not interfere with the transport system responsible for the accumulation of bile acids. In saponin-treated liver cells, PMA added before or after permeabilization failed to abolish TLC-induced Ca2+ release from the ER. The possibility is discussed that PMA, via PKC activation, may alter the intracellular binding or the transfer of bile acids in the liver.

Effect of phorbol esters and diacylglycerol on steroid metabolism in isolated rat hepatocytes

1988 ◽  
Vol 118 (1) ◽  
pp. 19-23 ◽  
Author(s):  
C. J. Allan ◽  
P. Skett
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Phorbol Ester ◽  
Phorbol Esters ◽  
Rat Hepatocytes ◽  
Male Rats ◽  
Steroid Metabolism ◽  
Isolated Rat Hepatocytes ◽  
Kinase C ◽  
Activate Protein Kinase

ABSTRACT Hepatocytes, isolated from adult male rats and maintained in serum- and hormone-free medium, were pretreated with phorbol esters known to activate protein kinase C (4β-phorbol-12-myristate-13-acetate) and to be inactive in this respect (4α-phorbol and its 12,13-didecanoate ester). Subsequently the cells were assayed for steroid-metabolizing capacity using androst-4-ene-3,17-dione as substrate. The active phorbol ester was seen to inhibit steroid metabolism markedly after 1 h whereas the inactive derivatives did not show this effect. The endogenous activator of protein kinase C (diacylglycerol) was also seen to inhibit steroid metabolism in a manner similar to the 4β-phorbol ester. Hepatic steroid metabolism is, thus, inhibited by activation of protein kinase C and this may be one of the mechanisms by which the regulatory hormones (e.g. growth hormone) affect steroid metabolism in the liver. J. Endocr. (1988) 118, 19–23

Phorbol esters and A23187 regulate Na+-K+-pump activity in pancreatic acinar cells

1987 ◽  
Vol 252 (4) ◽  
pp. G499-G505 ◽  
Author(s):  
S. R. Hootman ◽  
M. E. Brown ◽  
J. A. Williams
Keyword(s):  
Phorbol Ester ◽  
Phorbol Esters ◽  
Average Rate ◽  
Acinar Cells ◽  
Inhibitory Effect ◽  
Pancreatic Acinar Cell ◽  
Pancreatic Acinar Cells ◽  
Ionophore A23187 ◽  
Maximal Effect ◽  
Pump Activity

To clarify the subcellular mechanisms that mediate stimulation of Na+-K+-pump activity in pancreatic acinar cells by cholinergic agonists, we examined the effects of the phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA) and the Ca2+ ionophore A23187 on [3H]ouabain binding to dispersed guinea pig pancreatic acinar cells under conditions in which binding reflects the average rate of pump cycling. The phorbol ester more than doubled Na+-K+-pump activity as did the diacylglycerol analogue, 1-oleoyl-2-acetolyl-sn-3-glycerol. A23187 increased pump activity by a maximum of 31% at 0.3 microM but was progressively inhibitory at higher concentrations. The stimulatory effects of TPA and A23187 were additive, although either secretagogue elicited a less than additive response when added together with a maximally effective concentration of the cholinergic agonist, carbachol. Removal of extracellular Ca2+ had little effect on the pump response to TPA and did not reduce the maximal effect of A23187 but abolished the inhibitory effect seen at high ionophore concentrations in Ca2+-containing medium. These results indicate that both Ca2+ and protein kinase c are involved in regulating Na+-K+-pump activity in the pancreatic acinar cell.

Effects of extracellular ATP on hepatic fatty acid metabolism

1996 ◽  
Vol 270 (4) ◽  
pp. G701-G707 ◽  
Author(s):  
M. Guzman ◽  
G. Velasco ◽  
J. Castro
Keyword(s):  
Fatty Acid ◽  
De Novo ◽  
Specific Inhibitor ◽  
Rat Hepatocytes ◽  
Inhibitory Effect ◽  
Extracellular Atp ◽  
Acid Oxidation ◽  
A 23187 ◽  
Malonyl Coa ◽  
Cpt I

Incubation of rat hepatocytes with extracellular ATP inhibited acetyl-CoA carboxylase (ACC) activity and fatty acid synthesis de novo, with a concomitant decrease of intracellular malonyl-CoA concentration. However, both carnitine O-palmitoyltransferase I (CPT-I) activity and ketogenesis from palmitate were inhibited in parallel by extracellular ATP. The inhibitory effect of extracellular ATP on ACC and CPT-I activities was not evident in Ca2+ -depleted hepatocytes. Incubation of hepatocytes with thapsigargin, 2,5-di-(t-butyl)-1,4-benzohydroquinone (BHQ), or A-23187, compounds that increase cytosolic free Ca2+ concentration ([Ca2+]i), depressed ACC activity, whereas CPT-I activity was unaffected. The phorbol ester 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA) increased ACC activity, whereas it decreased CPT-I activity in a nonaddictive manner with respect to extracellular ATP. The inhibitory effect of extracellular ATP on ACC activity was also evident in the presence of bisindolyl-maleimide, a specific inhibitor of protein kinase C (PKC), whereas this compound abolished the extracellular ATP-mediated inhibition of CPT-I. In addition, the PMA-induced inhibition of CPT-I was not potentiated by thapsigargin, BHQ, or A-23187. Results thus show 1) that the intracellular concentration of malonyl-CoA is not the factor responsible for the inhibition of hepatic long-chain fatty acid oxidation by extracellular ATP, and 2) that the inhibition of ACC by extracellular ATP may be mediated by an elevation of [Ca2+]i, whereas CPT-I may be inhibited by extracellular ATP through a PKC-dependent mechanism.

PKC-independent inhibition of cardiac L-type Ca2+ channel current by phorbol esters

1996 ◽  
Vol 270 (2) ◽  
pp. H620-H627 ◽  
Author(s):  
T. Asai ◽  
L. M. Shuba ◽  
D. J. Pelzer ◽  
T. F. McDonald
Keyword(s):  
Protein Kinase C ◽  
Phorbol Esters ◽  
Ventricular Myocytes ◽  
Inhibitory Effect ◽  
Independent Action ◽  
Independent Manner ◽  
Channel Current ◽  
Kinase C ◽  
Channel Currents ◽  
Stimulation Of

Active and inactive phorbol esters were applied to guinea pig ventricular myocytes to study the responses of L-type Ca2+ (ICa,L) and L-type Na+ (INa,L) currents. Phorbol 12-myristate 13-acetate (PMA) (10-100 rM) never stimulated ICa,L or INa,L and frequently depressed them by 5-30% in a voltage-independent manner. However, the phorbol ester consistently activated delayed-rectifying K+ (IK) and Cl- currents. The inhibition of ICa,L occurred approximately 3 times faster than comonitored stimulation of IK, and ICa,L and INa,L were unaffected by two interventions that suppressed IK stimulation [pretreatment with 50 microM 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7) and dialysis with pCa 11 versus standard pCa 9 solution]. Inactive phorbol esters 4 alpha-phorbol 12,13-didecanoate (alpha-PDD) and 4 alpha-phorbol had little effect on IK, but alpha-PDD had a PMA-like inhibitory effect on Ca2+ channel currents. We conclude that, unlike the stimulation of IK by PMA, inhibition of Ca2+ channel current by phorbol esters is a protein kinase C-independent action.

Tamoxifen inhibits phorbol ester stimulated osteoclastic bone resorption: An effect mediated by calmodulin

2000 ◽  
Vol 78 (6) ◽  
pp. 715-723 ◽  
Author(s):  
John P Williams ◽  
Margaret A McKenna ◽  
Allyn M Thames III ◽  
Jay M McDonald
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Bone Resorption ◽  
Phorbol Ester ◽  
Phorbol Esters ◽  
Fold Increase ◽  
Dependent Manner ◽  
Osteoclast Activity ◽  
Kinase C ◽  
Protein Kinase Cα

Tamoxifen inhibits bone resorption by disrupting calmodulin-dependent processes. Since tamoxifen inhibits protein kinase C in other cells, we compared the effects of tamoxifen and the phorbol ester, phorbol myristate acetate, on osteoclast activity. Phorbol esters stimulate bone resorption and calmodulin levels four-fold (k0.5 = 0.1–0.3 µM). In contrast, tamoxifen inhibited osteoclast activity ~60% with an IC50 of 1.5 µM, had no apparent effect on protein kinase C activity in whole-cell lysates, and reduced protein kinase Cα recovered by immunoprecipitation 75%. Phorbol esters stimulated resorption in a time-dependent manner that was closely correlated with a similar-fold increase in calmodulin. Protein kinase Cα, β, δ, ε, and ζ were all down-regulated in response to phorbol ester treatment. Tamoxifen and trifluoperazine inhibited PMA-dependent increases in bone resorption and calmodulin by 85 ± 10%. Down-regulation of protein kinase C isoforms by phorbol esters suggests that the observed increases in bone resorption and calmodulin levels are most likely due to a mechanism independent of protein kinase C and dependent on calmodulin. In conclusion, the data suggest that protein kinase C negatively regulates calmodulin expression and support the hypothesis that the effects of both phorbol esters and tamoxifen on osteoclast activity is mediated by calmodulin.Key words: osteoclast, calmodulin, tamoxifen, osteoporosis, protein kinase C.

Bile canalicular contraction in the isolated hepatocyte doublet is related to an increase in cytosolic free calcium ion concentration

2008 ◽  
Vol 8 (3) ◽  
pp. 178-183 ◽  
Author(s):  
Sumio Watanabe ◽  
Masahiro Tomono ◽  
Makoto Takeuchi ◽  
Tsuneo Kitamura ◽  
Miyoko Hirose ◽  
...  
Keyword(s):  
Calcium Ion ◽  
Ion Concentration ◽  
Free Calcium ◽  
Cytosolic Free Calcium ◽  
Bile Canalicular Contraction ◽  
Calcium Ion Concentration
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