title: Platelet membrane alterations induced by the local anesthetic dibucaine.
abstract: Tertiary amine local anesthetics modify a variety of platelet membrane-related functions. The present study explored dibucaine (DB)-induced inhibition of platelet cohesion by examining structural and functional alterations of the human platelet membrane glycoprotein IIb-IIIa complex (GPIIb-IIIa) and platelet Ca2+ homeostasis. Complete inhibition of ADP-induced aggregation was achieved five minutes after platelet exposure to 0.10 to 0.25 mmol/L of DB when fibrinogen binding was reduced by 50%. At higher concentrations of DB (approximately 1 mmol/L), ADP-induced fibrinogen binding was completely blocked. Scatchard analysis revealed loss of high-affinity binding sites in addition to reduction in Bmax. In contrast, chymotrypsin-treated platelets sustained 50% inhibition of fibrinogen binding when incubated with 0.4 to 0.5 mmol/L DB, and kinetic analysis showed that the high-affinity platelet-fibrinogen interactions were reduced but not absent. Fibrinogen binding to chymotrypsin-treated platelets could not be completely inhibited even at high DB concentrations (1 mmol/L). The inhibition of fibrinogen binding to chymotrypsin-treated platelets correlated with changes in binding of a monoclonal antibody (10E5) specific for an epitope on the GPIIb-IIIa complex. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and radioelectroimmunoassay of DB-treated platelets, however, showed no evidence of a reduction or degradation of GP IIb or IIIa. Platelet incubation with DB (five minutes, 0.1 to 1.0 mmol/L) was also accompanied by: increased platelet membrane-associated Ca2+ involving low-affinity binding sites [Kd = 5 X 10(-5) mol/L-]; increased 45Ca2+ uptake which correlated with degradation of actin-binding protein (ABP) and digestion of GPIb as visualized on periodic-acid Schiff (PAS)-stained SDS gels and as inferred from decreased binding of a monoclonal antibody (6D1) directed against this glycoprotein; and enhanced Ca2+ exchange. Thus, exposure of platelets to DB results in membrane-related alterations that may contribute to inhibition of platelet cohesion: Decreased fibrinogen receptor exposure by traditional agonists and diminished accessibility of the GPIIb-IIIa complex to extracellular ligands correlate with DB-induced inhibition of platelet aggregation; and increased calcium uptake and exchange across the platelet membrane likely leads to activation of the calcium-dependent protease(s) which was previously shown to correlate with DB-induced inhibition of ristocetin-induced platelet agglutination.
mesh_terms: D001792:Blood Platelets / Q000166:cytology*; D002118:Calcium / Q000502:physiology; D002462:Cell Membrane / Q000166:cytology; D003992:Dibucaine / Q000494:pharmacology*; D006023:Glycoproteins / Q000378:metabolism; D006706:Homeostasis; D006801:Humans; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D010974:Platelet Aggregation / Q000187:drug effects; D010977:Platelet Factor 3 / Q000502:physiology; D010980:Platelet Membrane Glycoproteins; D011956:Receptors, Cell Surface / Q000187:drug effects
chemical_list: D006023:Glycoproteins; D010980:Platelet Membrane Glycoproteins; D011956:Receptors, Cell Surface; D010977:Platelet Factor 3; D007770:L-Lactate Dehydrogenase; D003992:Dibucaine; D002118:Calcium