Guanylate cyclase-cyclic GMP signaling pathway in platelet disaggregation associated with dissociation of PAF-receptor complex

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Continuous binding of the PAF molecule to its receptor is necessary for the long-term aggregation of human and rabbit platelets. On the other hand, human and rabbit platelets fully aggragated by PAF underwent slow disaggregation but were rapidly disaggregated by the PAF receptor antagonists WEB-2086 and Y-24180. PAF dissociated promptly from its receptor when Y-24180 was added, in parallel with elevation in platelet guanylate cyclase (GC) activity and intracellular cGMP level, followed by platelet disaggregation and disappearance of P-selectin on the cell surface, but no alteration in [Ca^<2+>]i. In addition, GC activator YC-1 (1 x 10^<-5> M) and cGMP phosphodiesterase inhibitor dipyridamole (3 x 10^<-6> M) suppressed PAF (2 x 10^<-10> M)-induced rabbit platelet aggregation, and moreover disaggregated the PAF-aggregated platelets by increasing intracellular cGMP level. CPT-cGMP (0.2 mM) but not CPT-cAMP (0.2 mM) also disaggregated PAF (2 x 10^<-10> M)-aggregated platelets. Whereas NO-d … More ependent soluble GC inhibitor ODQ (1 x 10^<-5> M) inhibited sodium nitroprusside-induced cGMP production in the platelets, ODQ did not affect the cGMP production when Y-24180 disaggregated PAF-aggregated platelets.We succeded in isolating a cDNA encoding PAF receptor from a human megakaryocytic cell line MEG01 and CMKII-5 cDNA, that is the same as neutrophile PAF receptor. Whereas platelets from PAF receptor+/+ mice were aggregated by PAF and the aggregation was blocked by PAF receptor antagonists, platelets from PAF receptor-/- mice were not aggregated by PAF. PAF antagonist Y24180 and Rho kinase inhibitor Y27632 synergistically disaggregated PAF-stimulted platelets. These results indicate that platelet PAF receptor is the same as that of neutrophile, but the signalling pathway through platelet PAF receptor is characteristic.In conclusion, these observations indicate that GC beside NO-dependent sGC plays an important role in signal transduction mechanism in platelet disaggregation associated with dissociation of PAF-receptor complex. Less