title: Dibucaine elicits platelet procoagulant activity in factor VIII and factor X activation by a mechanism involving a sulfhydryl-dependent enzyme.
abstract: Dibucaine, a potent inhibitor of platelet aggregation and platelet release, was found to enhance the ability of fresh gel-filtered or washed human platelets to support factor VIII activation and factor X activation. Dibucaine-treated platelets increased the peak of factor VIII clotting activity by 2-fold compared to activity with untreated platelets. Similarly platelets optimally stimulated by dibucaine (1.0-1.5 mM for 5 min at 37 degrees C) supported as much factor X activation by factors IXa and VIII (measured in a chromogenic assay) as platelets optimally stimulated by ionophore A23187 (15 microM). An assay of platelet calcium-dependent sulfhydryl proteases was devised and used to test the effect of various inhibitors on these platelet proteases. The membrane-permeable sulfhydryl inhibitor Thiolyte MB inhibited platelet calcium-dependent protease activity; whereas, membrane-impermeable Thiolyte MQ did not. Thiolyte MB also blocked the ability of dibucaine-stimulated platelets to support factor X activation. Incubation of fresh, gel-filtered platelets with calpain inhibitor II (N-Ac-L-L-Normethioninal) completely inhibited the calcium-dependent sulfhydryl protease activity of these platelets but did not affect their ability to support factor X activation after subsequent incubation with dibucaine. These data support the interpretation that an intracellular SH-dependent enzyme, which may not be calpain, is involved in the expression of platelet procoagulant activity in dibucaine-treated platelets.
authors.affiliation: Department of Medicine, State University of New York, Stony Brook.
authors.forename: M B
authors.initials: MB
authors.lastname: Hultin
authors.forename: J
authors.initials: J
authors.lastname: Hennessey
authors.forename: S A
authors.initials: SA
authors.lastname: Morrison
mesh_terms: D001643:Bridged Bicyclo Compounds / Q000494:pharmacology; D002154:Calpain / Q000037:antagonists & inhibitors; D003546:Cysteine Endopeptidases / Q000378:metabolism; D003992:Dibucaine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D005169:Factor VIII / Q000378:metabolism*; D005170:Factor X / Q000378:metabolism*; D006023:Glycoproteins; D006801:Humans; D015539:Platelet Activation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*
chemical_list: D001643:Bridged Bicyclo Compounds; D006023:Glycoproteins; D010975:Platelet Aggregation Inhibitors; C039304:calpain inhibitors; D005169:Factor VIII; D005170:Factor X; D002154:Calpain; D003546:Cysteine Endopeptidases; D003992:Dibucaine; C028381:monobromobimane