Role of tyrosine phosphorylation in regulation of inositol 1,4,5-trisphosphate-mediated Ca2+ release in human platelets.
Thrombin activation of human platelets is accompanied by tyrosine phosphorylation of many cellular proteins, as well as changes in the cytosolic Ca2+ concentration. Consequently, we assessed tyrosine phosphorylation of the platelet inositol 1,4,5-trisphosphate receptor (IP(3)R) to determine if phosphorylation modulates Ca2+ release from internal stores. Stimulation of platelets with thrombin resulted in tyrosine phosphorylation of the type 1 IP(3)R, which peaked at 3 min followed by dephosphorylation to the basal level by 10 min. Thrombin also increased the extent of IP(3)R-mediated Ca2+ release 1.6-fold in crude platelet membranes isolated from thrombin-stimulated (3 min) platelets. Since we have previously shown that the plasma membrane Ca2+-ATPase (PMCA) is also phosphorylated on tyrosine residues during thrombin-stimulated platelet activation, resulting in inhibition of the pump (Dean et al., J Biol Chem 1997; 272: 15113-9), the present results suggest that early in thrombin-stimulated platelet activation, tyrosine phosphorylation of PMCA and IP(3)R results in transient enhancement in platelet cytosolic Ca2+, but that this enhancement is attenuated by subsequent dephosphorylation.
Marian
M J
MJ
Department of Biochemistry and Molecular Biology, University of Louisville, Louisville, KY 40292, USA.
Dean
W L
WL