PHOSPHOLIPASE-D IN PLATELETS AND MEGAKARYOCYTIC CELLS

Phospholipase D (PLD) is stimulated in platelets by various agents. Ph osphatidylcholine is the major substrate for PLD. This enzymatic pathw ay generates phosphatidic acid selectively. Guanine nucleotides also s timulate PLD in platelet membranes. Furthermore, tyrosine kinase may a lso be involved in platelet PLD regulation. It appears that multiple s ignals acting sequentially or in parallel converge on PLD. Among other s, PLD has been proposed to play a role in platelet secretion and PLA( 2) regulation. PLD is also present in platelet percursor megakaryoctri c cells and can be activated by platelet agonists. In these cells both PKC and G-proteins (e.g. Rho) may regulate PLD activity. The signific ance of PLD in megakaryocytes awaits investigation. These recent devel opments offer new avenues of research to further elucidate the biochem istry of platelet and megakaryocyte function.