NOT CA2-CHANGES IN RAT MEGAKARYOCYTE( BUT CAMP IS THE 2ND MESSENGER FOR MORPHOLOGICAL)

ATP and thrombin both induced Ca2+ mobilization from intracellular Ca2 + store site of megakaryocyte, the progenitor cell of platelet (Uneyam a C., Uneyama H. and Akaike N. (1993) J. Physiol. (Lond.), 470,73-749) , Since in platelet, thrombin is known as a strong agonist and ADP is known as a weak agonist, we further investigated the effect of these a gonists on megakaryocyte. Thrombin induced Ca2+ mobilization, 5-hydrox y tryptamine (5-HT) release and aggregatory morphological changes in m egakaryocyte, but ATP induced only Ca2+ mobilization. Thrombin-induced 5-HT release was inhibited by adenylate cyclase-activating drugs, and the morphological changes could be induced by H-8, an inhibitor of cA MP-dependent protein kinase. These results suggest that the Ca2+ mobil ization is not sufficient to induce morphological changes, and the sig nal to cause morphological changes in megakaryocyte may be cAMP. (C) 1 995 Academic Press, Inc.