Release of calcium and P-selectin from intraplatelet granules is hampered by procaine

The inhibition of platelets by some local anaesthetics has been related to the modulation of platelet membrane lipid fluidity, and one of these compou nds, procaine, has been proven to be particularly effective inhibitor. In t he present study, we examined the effect of procaine on the mobilization of intracellular granule contents in isolated washed platelets. We revealed t hat the presence of 10 mg/ml procaine significantly hampered platelet relea se reaction, as demonstrated by the significant reduction in the expression of platelet P-selectin (CD62) on one hand, and significantly enhanced expr ession of GPIb alpha (CD42b) antigen on the other, following either 1 hour incubation of washed platelets at room temperature (%CD62: 37.1+/-6.8% of c ontrol incubated without procaine, p<<0.0001; % CD42b: 116.2+/-6.3% of cont rol, p<0.0001) or activation of whole blood platelets with ADP, TRAP, or th rombin. Procaine, which acted as a rigidizer, significantly decreased plate let membrane fluidity (ESR h(+1)/h(0) ratio of 5-DOXYL-Ste reduced down to 93.1+/-3.7% of control, p<0.001). In washed Fura-2-loaded platelets procain e not only brought about the significantly reduced Ca2+ release from intrap latelet storage pools after platelet stimulation with 15 mu mol/l ADP (25.3 +/-12.5% of control, p<0.001), but also it significantly increased the redu ction in Ca2+ concentration upon the addition of Ca2+ chelator, EDTAK(2) (4 8.9+/-13.5% vs. 40.9+/-12.1% of initial [Ca2+](i) concentration, p(1,alpha) <0.025). Overall, procaine considerably reduced calcium mobilization from i ntraplatelet storage pools and Ca2+ efflux across platelet membrane. Based on these data, we suggest that the preventive effects of procaine on platel et release reaction and calcium mobilization might relate to the changes in the organization of membrane components embedded into a lipid bilayer, whi ch are crucial in triggering of platelet release reaction. Procaine-mediate d dislocations of some membrane components and/or distortion of lipid-prote in interactions could generate a steric hindrance, which might interfere wi th platelet signal transduction, thus leading to impaired mobilization of C a2+ and other components from intraplatelet storage pools. (C) 1999 Elsevie r Science Ltd. All rights reserved.