u-44069 and 1-2-dioctanoylglycerol

Thrombin stimulation of human platelets is associated with turnover of inositol phospholipids, mobilization of intracellular Ca2+ stores, and activation of protein kinase C. However, within 5 minutes, the thrombin receptor desensitizes, but can be re-coupled to its effectors by stimulation of alpha 2-adrenergic receptors (Crouch and Lapetina, J. Biol. Chem. 263, 3363-3371, 1988). This effect of epinephrine was found to be inhibited by preincubation of platelets with phorbol ester, suggesting that protein kinase C was inhibitory. However, since thrombin also activated protein kinase C and epinephrine was active following thrombin stimulation of platelets, this implied that thrombin activation of protein kinase C may have been spacially isolated near the thrombin receptor and could not inactivate alpha 2-receptor activity. In the present paper, we have tested this possibility, and we present evidence which strongly favours the possibility that protein kinase C activation by receptors induces its local translocation to the cell membrane.

Topics: Blood Platelets; Blood Proteins; Calcium; Diglycerides; Enzyme Activation; Epinephrine; Fluorescent Dyes; Humans; Indoles; Kinetics; Phorbol 12,13-Dibutyrate; Phosphoproteins; Phosphorylation; Platelet Activating Factor; Prostaglandin Endoperoxides, Synthetic; Protein Kinase C; Thrombin