T Tohmatsu

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The effect of cyclic GMP (cGMP) on human platelet activation was investigated, using its metabolically stable analogue, 8-bromo cGMP (8-bcGMP). Thrombin-induced serotonin secretion was inhibited by pretreatment with 8bcGMP in a dose-dependent manner. Production of inositol trisphosphate (IP3), a Ca2+ releaser was inhibited by 8bcGMP pretreatment of(More)
The phospholipid metabolism of rat peritoneal mast cells stimulated with mastoparan, a secretagogue purified from wasp venom, was investigated. Mastoparan at 20 micrograms/ml caused a rapid secretion of histamine. Mastoparan induced a transient decrease of phosphatidylinositol 4,5-biphosphate on 32P labeling and generation of a water-soluble degradation(More)
Neomycin (10 microM - 1 mM) was found to induce considerable release of [3H]arachidonic acid from phosphatidylinositol, phosphatidylcholine and phosphatidylethanolamine in saponin-permeabilized human platelets prelabeled with [3H]arachidonic acid. The magnitude of arachidonate liberation was almost equal to that induced by A23187 (400 nM) or even greater(More)
Upon stimulation of human polymorphonuclear neutrophils with platelet-activating factor (PAF), arachidonic acid (AA) is released from membrane phospholipids. The mechanism for AA liberation, a key step in the synthesis of biologically active eicosanoids, was investigated. PAF was found to elicit an increase in the cytoplasmic level of free Ca2+ as monitored(More)
In the presence of 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7), a potent inhibitor of protein kinase C in vitro, phorbol-12-myristate-13-acetate (PMA) did not suppress the thrombin-induced increase of cytosolic Ca2+ concentration in human platelets. The H-7 reversal of the inhibitory action of PMA was also observed in thrombin-induced(More)
The phosphatidylinositol (PI) and phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolytic activities of phosphoinositide-specific phospholipase C (PLC) were measured in membrane and cytosol fractions from 7 discrete areas of the rat brain. Both the PI-PLC and PIP2-PLC specific activities were found to differ significantly among the 7 discrete brain areas.(More)
The hydrolysis of [3H]phosphatidylinositol 4,5-bisphosphate (PIP2) by cytosolic phospholipase C from human platelets was determined. Cytosolic fractions were prepared from platelets that had or had not been preactivated with thrombin. Thrombin pretreatment did not affect cytosolic phospholipase C activity. In both cytosolic fractions, phospholipase C was(More)
Ca2+ release triggered by inositol 1,4,5-trisphosphate (IP3) has been measured in saponin-permeabilized human platelets with quin2 or 45Ca2+. Ca2+ was sequestered by intracellular organelles in the presence of ATP, and IP3 released half of the sequestered Ca2+. The addition of cyclic AMP (cAMP) to permeabilized platelets transiently accelerated Ca2+(More)
The addition of arachidonic acid induced a rapid release of 45Ca2+ from human platelet membrane vesicles which accumulated 45Ca2+ in the presence of ATP. Docosahexaenoic acid, eicosapentaenoic acid, linolenic acid and linoleic acid were less active than arachidonic acid. In contrast, oleic acid, myristic acid and palmitic acid were without effect. The(More)
Rat peritoneal mast cells which had been preincubated with phorbol myristate acetate (PMA, 10 - 100 ng/ml) for 5 min did not elicit the full histamine secretion induced by a potent secretagogue, compound 48/80. Furthermore, this PMA-treatment was found to inhibit the agonist-mediated hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) in [32P]labeled(More)