cytochalasin-d and edelfosine

The role of the tyrosine kinase pp60src in PAR-1-dependent Ca2+ entry was investigated in human platelets. pp60src plays a role in thapsigargin (TG)-evoked store-operated Ca2+ entry (SOCE), which is thought to be a major component of thrombin-evoked Ca2+ entry.. pp60src tyr416 phosphorylation was used to assess pp60src activation. Fura-2-loaded platelets were used to monitor intracellular Ca2+ concentration ([Ca2+]i).. Activation of PAR-1 with the specific agonist SFLLRN increased pp60src activation within 10 s. This required phospholipase C (PLC) activity, Ca2+ release and a rise in intracellular Ca2+. PP2, an inhibitor of Src-family tyrosine kinases, inhibited SFLLRN-evoked Ca2+ entry, but also inhibited Ca2+ release and the extrusion of Ca2+ by the plasma membrane Ca2+ ATPase. Actin polymerization and conventional protein kinase C (cPKC) activity were required for TG- and SFLLRN-evoked pp60src activation. Although Gö6976, an inhibitor of cPKCs, inhibited TG-evoked SOCE, it had little effect on SFLLRN- or thrombin-evoked Ca2+ entry.. These data indicate that stimulation of PAR-1 leads to activation of pp60src in human platelets, through PLC and cPKC activation, Ca2+ release and actin polymerization. However, as PKC and actin polymerization are not needed for SFLLRN-evoked Ca2+ entry, we suggest that pp60src is also not required. The apparent inhibition of SFLLRN-evoked Ca2+ entry by PP2 is likely to be secondary to reduced Ca2+ release. These data argue against a contribution of this SOCE pathway to PAR-1-dependent Ca2+ entry.

Topics: Actins; Blood Platelets; Calcium; Calcium Signaling; Carbazoles; Chelating Agents; Cytochalasin D; Cytoskeleton; Egtazic Acid; Enzyme Activation; Enzyme Inhibitors; Humans; In Vitro Techniques; Indoles; Peptide Fragments; Phospholipid Ethers; Phosphorylation; Plasma Membrane Calcium-Transporting ATPases; Protein Kinase C; Proto-Oncogene Proteins pp60(c-src); Pyrimidines; Receptor, PAR-1; Sarcoplasmic Reticulum Calcium-Transporting ATPases; Thapsigargin; Time Factors; Type C Phospholipases