ERK activation by Ca2+ionophores depends on Ca2+entry in lymphocytes but not in platelets, and does not conduct membrane scrambling

Rapid Ca2+- dependent phospholipid ( PL) reorganization ( scrambling) at the plasma membrane is a mechanism common to hematopoietic cells exposing procoagulant phosphatidylserine ( PS). The aim of this research was to determine whether activation of the extracellular signal- regulated kinase ( ERK) pathway was required for PL scrambling, based on a single report analyzing both responses induced by Ca2+ ionophores in megakaryoblastic HEL cells. Ca2+ ionophore- stimulated ERK phosphorylation was induced in platelets without external Ca2+, whereas exogenous Ca2+ entry was crucial for ERK activation in Jurkat T cells. In both cells, membrane scrambling only occurred following Ca2+ entry and was not blocked by inhibiting ERK phosphorylation. Furthermore, ERK proteins are strongly phosphorylated in transformed B lymphoblastic cell lines, which do not expose PS in their resting state. Overall, the data demonstrated that ERK activation and membrane scrambling are independent mechanisms.