THROMBIN INTERACTIONS WITH CELLS OF THE MEGAKARYOCYTIC LINEAGE

Thrombin is a potent physiological platelet agonist, critical for haem ostasis and thrombosis. Several studies have recently demonstrated tha t thrombin also displays functional effects on bone marrow platelet pr ogenitors, i.e. the megakaryocytes, and possibly on megakaryocyte prec ursors. Following a brief description of the different cell systems us ed for these investigations, this paper focuses on data related to thr ombin receptors, their coupling mechanisms, and biological responses d ue to their activation on cells of the megakaryocytic lineage. In spit e of some differences, whose significance remains to be established, m ost data reported give evidence of considerable homologies in thrombin receptors and signal transduction mechanisms between platelets and ce lls belonging to the megakaryocytic lineage. In addition, a potential functional role for thrombin in the regulation of megakaryocytopoiesis is emerging. The physiological relevance of these observations are di scussed.