Relationship between structure of phenothiazine analogues and their activity on platelet calcium fluxes

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Abstract
1 Phenothiazine analogues have been tested for their effect on calcium uptake into platelet membrane vesicles and on ionophore-induced platelet activation, both phenomena being Ca2+-dependent. 2 Both calcium uptake into membrane vesicles and ionophore-induced platelet activation were inhibited by the drugs. 3 Evidence for two inhibitors as potent as chlorpromazine and trifluoperazine was found. 4 These drugs are apparently competitive inhibitors of calcium uptake. 5 A structure-activity relationship has been established. 6 The data suggest that the phenothiazines are able to inhibit calmodulin-insensitive calcium uptake of platelet membrane vesicles and that therefore they cannot be assumed to be selective inhibitors of calmodulin interactions under all circumstances.