title: Effect of trifluoperazine, compound 48/80, TMB-8 and verapamil on the rate of calmodulin binding to erythrocyte Ca2+-ATPase.
abstract: The erythrocyte Ca2+-ATPase shifts reversibly between two states, the calmodulin-deficient A-state and the calmodulin-saturated B-state, dependent on calcium and calmodulin. The effects on this system of the four drugs, trifluoperazine, compound 48/80, TMB-8 and verapamil were studied. All four drugs inhibited the maximum activity of the B -state Ca2+-ATPase and, in addition, trifluoperazine and compound 48/80 in higher doses inhibited the A-state. Furthermore, the four drugs decreased the calmodulin sensitivity of the Ca2+-ATPase in the order of decreasing effect: trifluoperazine greater than compound 48/80 greater than TMB-8 greater than verapamil. In the same order of decreasing effect the drugs increased the time required for full calmodulin activation of the A-state of Ca2+-ATPase, whereas the drugs had only small effects on the rate of deactivation of the B-state, caused by dissociation of calmodulin from the enzyme. It is discussed whether the effects on calmodulin activation were caused by a reduction of free calmodulin due to the formation of drug-calmodulin complexes or whether the drugs, especially trifluoperazine, compound 48/80 and TMB-8, by binding to the Ca2+-ATPase, decreased the rate constants for association of calmodulin and enzyme.
mesh_terms: D002121:Calcium Channel Blockers / Q000494:pharmacology*; D000252:Calcium-Transporting ATPases / Q000097:blood*; D002147:Calmodulin / Q000097:blood*; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000201:enzymology*; D005707:Gallic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D014268:Trifluoperazine / Q000494:pharmacology*; D014700:Verapamil / Q000494:pharmacology; D003189:p-Methoxy-N-methylphenethylamine / Q000494:pharmacology*
chemical_list: D002121:Calcium Channel Blockers; D002147:Calmodulin; D014268:Trifluoperazine; D003189:p-Methoxy-N-methylphenethylamine; C006014:8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate; D005707:Gallic Acid; D014700:Verapamil; D000252:Calcium-Transporting ATPases