Collagen or collagen-related peptide cause (Ca2+)(i) elevation and increased tyrosine phosphorylation in human megakaryocytes

Since megakaryocytes are the cellular precursors of platelets we have inves tigated whether they share responses to platelet agonists, in particular co llagen. Although previous studies have reported responses to thrombin in no n-human megakaryocytes, through studies of single cell calcium responses an d protein tyrosine-phosphorylation we demonstrate for the first time that b oth isolated human megakaryocytes and CD41/61-positive megakaryocytes deriv ed in culture from CD34+ cells share responses to the platelet agonists col lagen, collagen-related peptide and thrombin. The responses to either colla gen or CRP were seen only in the most mature megakaryocytes and not in mega karyocyte-like cell lines, suggesting that the response to collagen is a ch aracteristic developed late during megakaryocyte differentiation. Those pri mary cells offer the opportunity to use many molecular and cellular techniq ues to study and manipulate signalling events in response to platelet recep tor agonists, which cannot be performed in the small, anucleate platelet it self.