Cytosolic calcium mobilization and thromboxane synthesis in a human megakaryocytic leukemia cell

The functional and biochemical characteristics of human megakaryocytic leukemia cells remain unclear. In this study, we examined cytosolic Ca2+ ([Ca2+]i) mobilization and thromboxane (TX) formation in a megakaryocytic leukemia cell line, designated CMK. Stimulation of CMK cells with thrombin resulted in an increase of [Ca2+]i as measured with the fluorescent marker Fura 2-AM. The rise in [Ca2+]i was mostly dependent on extracellular Ca2+. Prostaglandin E1 (PGE1) further increased [Ca2+]i after thrombin addition, thus indicating that PGE1 had a different action on [Ca2+]i in cells of the platelet-megakaryocyte lineage. The addition of thrombin and the calcium ionophore A23178 to CMK cells caused similar rapid formations of TXB2 as measured by RIA. Thrombin plus A23178 had a synergistic effect on TXB2 synthesis in CMK cells. Thrombin had no effect of TX metabolism in the cells with myeloid, erythroid, B-lymphoid, and T-lymphoid lineages. These results indicate that thrombin-induced TX synthesis may serve as a marker of immature megakaryocytes.