ORIGINAL ARTICLES   

International Angiology 1998 March;17(1):38-42

Copyright © 2000 EDIZIONI MINERVA MEDICA

language: English

Decrease of platelet intracellular pH and adhesion by ticlopidine in patients with vascular disease

Lechi C., Gaino S., Andrioli G., Paluani F., Guzzo P., Bellavite P., Zatti M., Arosio E.

From the * Institute of Medical Clinics and Chemistry and Clinic Microscopics, University of Verona, Italy

Background. Ticlopidine inhib­its plate­let aggre­ga­tion by pre­vent­ing the bind­ing of fibrino­gen to its plate­let recep­tor. We exam­ined wheth­er this inhi­bi­tion ­involved plate­let trans­duc­tion ­system such as Na+/H+ pump and plate­let intra­cel­lu­lar cal­cium.
Methods. Platelet adhe­sion in 13 ­patients with periph­er­al vas­cu­lar dis­ease treat­ed with ticlop­i­dine, 250 mg b.i.d for 30 days, was meas­ured in cul­ture micro­plates ­before and after ther­a­py. The micro­plate wells were coat­ed with human plas­ma, fibrino­gen or col­la­gen, and platelet adhesion was studied in the rest­ing con­di­tion and after stim­u­la­tion with 1 and 10 µM ADP. At the same time, plate­let intra­cel­lu­lar cal­cium and ADP-­induced cal­cium ­increases were meas­ured with the flu­o­res­cent indi­ca­tor Fura 2. In addi­tion, intra­cel­lu­lar pH and throm­bin-­induced pH vari­a­tions were meas­ured with the flu­o­res­cent probe BCECF.
Results. Platelet adhe­sion to plas­ma and fibrino­gen was sig­nif­i­cant­ly ­reduced (about 50%) after treat­ment with ticlop­i­dine, while adhe­sion to col­la­gen was not mod­i­fied. Basal cal­cium and ADP-­induced cal­cium ­increase were not sig­nif­i­cant­ly dif­fer­ent ­before and after ticlop­i­dine. Platelet basal intra­cel­lu­lar pH was ­reduced (from 7.44±0.009 to 7.41±0.017, p<0.05), but ago­nist-­induced alka­lin­isa­tion was not sig­nif­i­cant­ly dif­fer­ent. Early acid­ifi­ca­tion, not depen­dent on Na+/H+ ­exchange, was also ­reduced (p<0.05).
Conclusions. These data do not seem to sup­port the hypoth­e­sis that ticlop­i­dine-­induced reduc­tion of plate­let adhe­sion ­depends on alter­a­tion of the mech­a­nisms deter­min­ing sig­nal trans­duc­tion, at least as far as basal and post-stim­u­la­tion intra­cel­lu­lar cal­cium is con­cerned. On the con­trary, the pos­sibil­ity that ticlop­i­dine inhib­its the Na+/H+ anti­port ­remains open to con­sid­er­a­tion.