The inflammatory and tumor-promoting sesquiterpene lactone, thapsigargin, activates platelets by selective mobilization of calcium as shown by protein phosphorylations
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The inflammatory and tumor-promoting sesquiterpene lactone, thapsigargin, activates platelets by selective mobilization of calcium as shown by protein phosphorylations. / Thastrup, Ole; Linnebjerg, H; Bjerrum, P J; Knudsen, J B; Christensen, S B.
In: BBA General Subjects, Vol. 927, No. 1, 1987, p. 65-73.Research output: Contribution to journal › Journal article › Research › peer-review
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T1 - The inflammatory and tumor-promoting sesquiterpene lactone, thapsigargin, activates platelets by selective mobilization of calcium as shown by protein phosphorylations
AU - Thastrup, Ole
AU - Linnebjerg, H
AU - Bjerrum, P J
AU - Knudsen, J B
AU - Christensen, S B
PY - 1987
Y1 - 1987
N2 - We have studied the activation of human blood platelets by the inflammatory and tumor-promoting sesquiterpene lactone, thapsigargin. The effect of thapsigargin was compared with other common agonists (calcium ionophore A23187, phorbol ester TPA and thrombin). Platelet aggregation, serotonin release, raised cytoplasmic free calcium level and phosphorylation of platelet proteins was examined in platelet-rich plasma and washed platelet suspension. In contrast to A23187 and thrombin, the platelet activation induced by thapsigargin developed slowly, with maximal response obtained after 2-3 min. Both the thapsigargin- and the A23187-induced serotonin releases were synergistically increased by TPA. Studies of the phosphorylation of platelet proteins revealed that thapsigargin and A23187 equally well induced a selective phosphorylation of two proteins with apparent molecular masses of 20 kDa and 47 kDa. These proteins, which are substrates of myosin light-chain kinase and protein kinase C respectively, are known to be involved in platelet activation. The thapsigargin-induced platelet aggregation and serotonin release was completely inhibited by class I (nimodipine), class II (verapamil) and class III (diltiazem) calcium-channel blockers. The inhibitory activity of nimodipine was abolished by the corresponding 1,4-dihydropyridine calcium-channel agonist, BAY K 8644. These results shows that the thapsigargin-induced platelet activation is mediated by an increase in the cytoplasmic free calcium level, presumably obtained by stimulation of the passive calcium transport through specific channels. These thapsigargin-sensitive channels should predominantly be located in the membranes of intracellular calcium stores rather than in the plasma membrane, because removal of extracellular calcium by EGTA had only an insignificant effect on the thapsigargin-induced rise in cytoplasmic free calcium level.
AB - We have studied the activation of human blood platelets by the inflammatory and tumor-promoting sesquiterpene lactone, thapsigargin. The effect of thapsigargin was compared with other common agonists (calcium ionophore A23187, phorbol ester TPA and thrombin). Platelet aggregation, serotonin release, raised cytoplasmic free calcium level and phosphorylation of platelet proteins was examined in platelet-rich plasma and washed platelet suspension. In contrast to A23187 and thrombin, the platelet activation induced by thapsigargin developed slowly, with maximal response obtained after 2-3 min. Both the thapsigargin- and the A23187-induced serotonin releases were synergistically increased by TPA. Studies of the phosphorylation of platelet proteins revealed that thapsigargin and A23187 equally well induced a selective phosphorylation of two proteins with apparent molecular masses of 20 kDa and 47 kDa. These proteins, which are substrates of myosin light-chain kinase and protein kinase C respectively, are known to be involved in platelet activation. The thapsigargin-induced platelet aggregation and serotonin release was completely inhibited by class I (nimodipine), class II (verapamil) and class III (diltiazem) calcium-channel blockers. The inhibitory activity of nimodipine was abolished by the corresponding 1,4-dihydropyridine calcium-channel agonist, BAY K 8644. These results shows that the thapsigargin-induced platelet activation is mediated by an increase in the cytoplasmic free calcium level, presumably obtained by stimulation of the passive calcium transport through specific channels. These thapsigargin-sensitive channels should predominantly be located in the membranes of intracellular calcium stores rather than in the plasma membrane, because removal of extracellular calcium by EGTA had only an insignificant effect on the thapsigargin-induced rise in cytoplasmic free calcium level.
KW - Blood Platelets
KW - Calcimycin
KW - Calcium
KW - Cytoplasm
KW - Diltiazem
KW - Humans
KW - Kinetics
KW - Molecular Weight
KW - Nimodipine
KW - Phosphoproteins
KW - Plant Extracts
KW - Platelet Aggregation
KW - Serotonin
KW - Tetradecanoylphorbol Acetate
KW - Thapsigargin
KW - Thrombin
KW - Verapamil
M3 - Journal article
C2 - 3098302
VL - 927
SP - 65
EP - 73
JO - B B A - General Subjects
JF - B B A - General Subjects
SN - 0304-4165
IS - 1
ER -
ID: 43350572