Inactivation of platelet glycoprotein IIb/IIIa receptor by nitric oxide donor 3-morpholino-sydnonimine.

Nitric oxide (NO) is known to modulate platelet adhesion and aggregation, which are both mediated by fibrinogen receptor glycoprotein (GP)IIb/IIIa. To investigate effects of NO on GPIIb/IIIa activation and inactivation, platelets were exposed to NO donor 3-morpholino-sydnonimine (SIN-1) before and after stimulation with different agonists: thromboxane analog U-46619, epinephrine, adenosine diphosphate, human a-thrombin, and phorbol-12-myristate-13-acetate (0.02 micromol/l). (1) Flow cytometry analysis of SIN-1-pre-incubated samples using PAC-1 monoclonal antibody revealed an inhibition of receptor activation by 80.9 +/- 1.2, 71.3 +/- 1.8, 56 +/- 4.9, 87 +/- 3.4, and 56 +/- 5% (mean +/- SEM, relative to baseline). (2) Administration of SIN-1 after stimulation reversed receptor activation by 55 +/- 5.2, 56 +/- 2.0, 53 +/- 5.4, 42 +/- 4.3, and 44 +/- 5%, respectively. With 0.1 micromol/l phorbol-12-myristate-13-acetate, GPIIb/IIIa activation was irreversible. (3) SIN-1 effects could completely be blocked by equimolar addition of guanylyl cyclase inhibitor 1H(1,2,4)oxadiazolo(4,3-alpha)quinoxalin-1-on. (4) Spontaneous receptor closure after activation with human alpha-thrombin and adenosine diphosphate was not due to platelet-derived NO; SIN-1, however accelerated spontaneous receptor inactivation. (5) SIN-1-inactivated receptors still responded to stimulation. In conclusion, SIN-1 or NO modulates GPIIb/IIIa conformational change in vitro via guanosine 3',5'-monophosphate-dependent pathways. Whereas spontaneous receptor inactivation may be enhanced by exogenous NO, platelet-derived NO is not involved in receptor inactivation.