INVOLVEMENT OF GUANYLATE-CYCLASE AND PHOSPHODIESTERASES IN THE FUNCTIONAL-HETEROGENEITY OF HUMAN BLOOD-PLATELET SUBPOPULATIONS

Cyclic nucleotides are involved in the regulation of platelet activati on, shape change, and aggregation. In this study we have investigated the role of guanylate cyclase and phosphodiesterase in three functiona l heterogeneous human blood platelet subpopulations separated accordin g to density. In low-density platelets aggregation was enhanced and in hibited less when cyclic GMP was increased by sodium nitroprusside, co mpared to high-density platelets. Low-density platelets possessed a lo wer basal level of cyclic GMP and exhibited a smaller increase in cycl ic GMP after stimulation with sodium nitroprusside. Cyclic GMP-depende nt phosphodiesterase activity was similar in high, low, and intermedia te-density platelets. In contrast, the activity of the cyclic AMP-depe ndent phosphodiesterase was higher in low-density compared to high and intermediate-density platelets. These results suggest that regulation of cyclic GMP and cyclic AMP levels plays an important role in the fu nctional heterogeneity of human blood platelets.