Platelet membrane alterations induced by the local anesthetic dibucaine
EI Peerschke
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.
Volume 68,
Issue 2,
pp. 463-471,
08/01/1986
Copyright © 1986 by The American Society of Hematology
