Verapamil Inhibits Platelet Aggregation by a Calcium-Independent Mechanism

1986 ◽  
Vol 56 (03) ◽  
pp. 308-310 ◽  
Author(s):  
Giovanni Bonadonna ◽  
Clara Lechi ◽  
Paola Corradini ◽  
Daniela Sinigaglia ◽  
Piero De Togni ◽  
...  
Keyword(s):  
Protein Kinase C ◽  
Platelet Aggregation ◽  
Channel Blocker ◽  
Inhibitory Effects ◽  
Myristate Acetate ◽  
Fluorescent Indicator ◽  
Inhibition Of Platelet Aggregation ◽  
Kinase C ◽  
Aggregation Response ◽  
Independent Mechanism

SummaryWe studied the inhibitory effects of the calcium channel blocker verapamil both on platelet aggregation and intracellular calcium [Ca2+]i in platelets loaded with a fluorescent indicator (quin 2).The inhibitory effects of verapamil on the platelet aggregation response to both thrombin and ionomycin were seen to be clearly dissociated from the verapamil-induced inhibition of the [Ca2+]i increase produced by these agonists. Verapamil-induced inhibition of platelet aggregation was also obtained when using the “calcium-independent” agonist phorbol-myristate acetate (PMA). It may be deduced that a calcium-independent mechanism plays a role in verapamil-induced inhibition of platelet aggregation. We postulate that this mechanism may operate via a protein-kinase C pathway.

R59022, A DIACYLGLYCEROL (DG) KINASE INHIBITOR POTENTIATES THROMBIN-INDUCED PLATELET AGGREGATION AND GRANULE RELEASE

1987 ◽  
Author(s):  
S K Joseph ◽  
S Krishnamurthi ◽  
V V Kakkar
Keyword(s):  
Protein Kinase C ◽  
Platelet Aggregation ◽  
Kinase Inhibitor ◽  
Human Platelets ◽  
Maximal Concentration ◽  
Inhibitory Effects ◽  
Kinase C ◽  
Granule Secretion ◽  
Granule Release

R59022 is a recently described inhibitor of the enzyme DG kinase [1], which converts DG to phosphatidic acid. While R59002 inhibits DG conversion in platelets resulting in enhanced protein kinase C (PrkC) activation [1], little is known on its effect on other platelet responses. In this study, we have examined the effect of R59022 on agonist-induced platelet aggregation and [14C]-5-hydroxytryptamine (5HT) release using washed human platelets. With a sub-maximal concentration of thrombin (T, 0.05U/ml) R59022 (10-30μM) significantly potentiated T-induced platelet aggregation and [14C]-5HT release eg % [14C]-5HT release:- 0.05U/ml T-52±5,30μM R59022+T-76±8. Removal of external Ca2+ (ImM) using EGTA (5mM) reduced T-induced 5HT release but not the potentiation of it by R59022 eg EGTA+ 0.05U/ml T-36±6%, EGTA+R59022+T- 72±5%. These results show that in the presence of EGTA and R59022 the increased DG levels can compensate for the diminished rise in T-induced Ca/2+ mobilisation thus re-emphasizing the importance of DG in promoting granule secretion. In addition to inhibiting DG phosphorylation, R59022 also inhibits the phosphorylation of the DG analogue 1-oleoyl 2-acetylglycerol (OAG) [1]. OAG (63μM) with pre-incubation times of 10-60 sec, significantly potentiated threshold T (0.03U/ml)-induced [l4C]-5HT release, though with longer incubation times, this potentiatory effect was gradually lost eg 0.03U/ml T-l±0.3%, OAG+T (10 sec)- 33±4%, OAG+T (1 min)-11±3%, 0AG+veh.-0%. However, in the presence of R59022 (30μM), OAG retained its potentiatory effect for longer periods eg R59022+0AG+T (1 min)-45+10%, R59022+T-2±l%. With incubation times > 5 min the potentiatory effects of OAG were lost even in the presence of R59022. This is possibly due to the metabolism of OAG by DG lipase. Our results demonstrate that R59022, which has been reported to inhibit DG kinase leading to enhanced PrkC activation, also enhances agonist-induced platelet aggregation and 5HT release. It may therefore be a useful compound in elucidating further the role of DG in terms of both stimulatory and inhibitory effects on platelet activation.[1]. de Chaffoy de Coucelles, D. et al (1985) J Biol Chem 260, 15762.

Inhibitory Effects of Resveratrol on Platelet Activation Induced by Thromboxane A2Receptor Agonist in Human Platelets

2011 ◽  
Vol 39 (01) ◽  
pp. 145-159 ◽  
Author(s):  
Yumin Yang ◽  
Xiaoling Wang ◽  
Li Zhang ◽  
Huiping An ◽  
Zhigao Zao
Keyword(s):  
Protein Kinase C ◽  
Platelet Aggregation ◽  
Protein Kinase ◽  
Red Wine ◽  
Human Platelets ◽  
Dependent Manner ◽  
Inhibitory Effects ◽  
Signal Transduction System ◽  
Concentration Dependent Manner ◽  
Kinase C

Resveratrol (RSVL), a polyphenolic compound found in red wine is believed to be a contributor in decreasing the incidence of coronary heart disease. Although its primary target is unknown, it blocks platelet aggregation by an ill-defined mechanism. Protein kinase C (PKC), which would redistribute from the cytosol to the platelet membrane upon platelet stimulation, plays a key role in the signal transduction system of platelets in human. In this study, we investigated the effect of RSVL and a PKC inhibitor (DL-erythro-1,3-Dihydroxy-2-aminooctadecane, PKCI) on platelet aggregation induced by a thromboxane A2receptor agonist (U46619, 9,11-Dideoxy-11α, 9α-epoxymethanoprostaglandin F2α) using a platelet aggregometer. We also studied the platelet membranebound fibrinogen (PFig) content and the activity of protein kinase C (PKC) in platelets from healthy volunteers using flow cytometry, and a phosphorimaging system, respectively. Our results showed that RSVL blocked platelet aggregation and PFig content induced by U46619 in a concentration-dependent manner. PKCI and RSVL had an additive effect in inhibiting platelet aggregation and PFig content. Furthermore, RSVL (final concentration 50 μM) remarkably depressed the activity of PKC in the membrane of platelets and the percentage of membrane PKC activity in total PKC activity. Taken together, these results suggested that RSVL suppressed U46619-induced platelet aggregation and PFig content partially through the inhibition of the activity of PKC in platelets.

Chronic treatment by the calcium channel blocker ± PN 200-110 in the rat counteracts the stimulations of pituitary weight, prolactin release and pituitary C-kinase activity induced by a chronic estradiol treatment, in vivo

1990 ◽  
Vol 122 (3) ◽  
pp. 403-408
Author(s):  
Ph. Touraine ◽  
P. Birman ◽  
F. Bai-Grenier ◽  
C. Dubray ◽  
F. Peillon ◽  
...  
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Calcium Channel ◽  
Calcium Channel Blocker ◽  
Channel Blocker ◽  
Plasma Prolactin ◽  
Estradiol Treatment ◽  
Kinase C ◽  
Protein Kinase C Activity

Abstract In order to investigate whether a calcium channel blocker could modulate the protein kinase C activity in normal and estradiol pretreated rat pituitary, female Wistar rats were treated or not (controls) with ± PN 200-110 (3 mg · kg−1 · day−1, sc) for 8 days or with estradiol cervical implants for 8 or 15 days, alone or in combination with PN 200-110 the last 8 days. Estradiol treatment induced a significant increase in plasma prolactin levels and pituitary weight. PN 200-110 administered to normal rats did not modify these parameters, whereas it reduced the effects of the 15 days estradiol treatment on prolactin levels (53.1 ± 4.9 vs 95.0 ±9.1 μg/l, p<0.0001) and pituitary weight (19.9 ± 0.4 vs 23.0 ± 0.6 mg, p <0.001), to values statistically comparable to those measured after 8 days of estradiol treatment. PN 200-110 alone did not induce any change in protein kinase C activity as compared with controls. In contrast, PN 200-110 treatment significantly counteracted the large increase in soluble activity and the decrease in the particulate one induced by estradiol between day 8 and day 15. We conclude that PN 200-110 opposed the stimulatory effects of chronic in vivo estradiol treatment on plasma prolactin levels and pituitary weight and that this regulation was related to a concomitant modulation of the protein kinase C activity.

Effect of phorbol myristate acetate on secretion of parathyroid hormone

1988 ◽  
Vol 254 (1) ◽  
pp. E63-E70 ◽  
Author(s):  
J. J. Morrissey
Keyword(s):  
Protein Kinase C ◽  
Parathyroid Hormone ◽  
Protein Kinase ◽  
Membrane Fraction ◽  
Hormone Secretion ◽  
Myristate Acetate ◽  
Kinase C ◽  
Low Calcium ◽  
Protein Kinase C Activity ◽  
High Calcium

The influence of phorbol myristate acetate (PMA), an activator of protein kinase c, on the secretion of parathyroid hormone from collagenase-dispersed bovine parathyroid cells was tested. The cells were incubated at low (0.5 mM) or high (2.0 mM) concentrations of calcium in the medium, and the hormone secreted into the medium was measured by a radioimmunoassay that recognizes both intact and C-terminal fragments of hormone. At low calcium, the secretory rate averaged 32 +/- 3.8 ng.h-1.(10(5) cells)-1. The addition of 1.6 microM PMA did not affect secretion. At high calcium there was a significant suppression of secretion by 38% to 19.8 +/- 3 ng.h-1.(10(5) cells)-1. The addition of 1.6 microM PMA significantly stimulated hormone secretion to 35.8 +/- 8 ng.h-1.(10(5) cells)-1, a rate indistinguishable from low calcium. This stimulatory effect of PMA at high calcium was seen at PMA concentrations as low as 1.6 nM, did not occur with a biologically inactive 4 alpha-isomer of phorbol ester, and was independent of changes in cellular adenosine 3',5'-cyclic monophosphate levels. Examination of 32P-labeled phosphoproteins by two-dimensional gel electrophoresis revealed acidic proteins of approximately 20,000 and 100,000 Da that were phosphorylated at low and high calcium + 1.6 microM PMA but not at high calcium alone. The protein kinase c activity associated with the membrane fraction of parathyroid cells significantly decreased 40% when the cells were incubated at high vs. low calcium. The data suggest that calcium may regulate parathyroid hormone secretion through changes in protein kinase c activity of the membrane fraction of the cell and protein phosphorylation.

scholarly journals Prostacyclin inhibits platelet aggregation induced by phorbol ester or Ca2+ ionophore at steps distal to activation of protein kinase C and Ca2+-dependent protein kinases

1989 ◽  
Vol 258 (1) ◽  
pp. 57-65 ◽  
Author(s):  
W Siess ◽  
E G Lapetina
Keyword(s):  
Protein Kinase C ◽  
Platelet Aggregation ◽  
Protein Kinase ◽  
Protein Kinases ◽  
Shape Change ◽  
Ionophore A23187 ◽  
Maximal Effect ◽  
Kinase C ◽  
Dependent Protein ◽  
High Concentrations

Suspensions of aspirin-treated, 32P-prelabelled, washed platelets containing ADP scavengers in the buffer were activated with either phorbol 12,13-dibutyrate (PdBu) or the Ca2+ ionophore A23187. High concentrations of PdBu (greater than or equal to 50 nM) induced platelet aggregation and the protein kinase C (PKC)-dependent phosphorylation of proteins with molecular masses of 20 (myosin light chain), 38 and 47 kDa. No increase in cytosolic Ca2+ was observed. Preincubation of platelets with prostacyclin (PGI2) stimulated the phosphorylation of a 50 kDa protein [EC50 (concn. giving half-maximal effect) 0.6 ng of PGI2/ml] and completely abolished platelet aggregation [ID50 (concn. giving 50% inhibition) 0.5 ng of PGI2/ml] induced by PdBu, but had no effect on phosphorylation of the 20, 38 and 47 kDa proteins elicited by PdBu. The Ca2+ ionophore A23187 induced shape change, aggregation, mobilization of Ca2+, rapid phosphorylation of the 20 and 47 kDa proteins and the formation of phosphatidic acid. Preincubation of platelets with PGI2 (500 ng/ml) inhibited platelet aggregation, but not shape change, Ca2+ mobilization or the phosphorylation of the 20 and 47 kDa proteins induced by Ca2+ ionophore A23187. The results indicate that PGI2, through activation of cyclic AMP-dependent kinases, inhibits platelet aggregation at steps distal to protein phosphorylation evoked by protein kinase C and Ca2+-dependent protein kinases.

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