Arachidonic acid is preferentially incorporated by immature megakaryocytes

Abstract

Megakaryocytes are bone marrow cells responsible for the synthesis of circulating platelets. Subgroups of megakaryocytes can be recognized on the bases of morphologic stage, DNA content (ploidy), and size. However, the physiologic roles and biochemical characteristics of these subgroups have not been defined. We have investigated arachidonic acid uptake in megakaryocyte subgroups. Purified guinea pig megakaryocytes were incubated with tritiated arachidonic acid, cytocentrifuged, and subjected to autoradiography. Eight hundred megakaryocytes were analyzed in four experiments by four parameters: (1) grains per cell (arachidonic acid uptake), (2) ploidy, (3) morphologic stage, and (4) size. Lipids were extracted from aliquots of megakaryocytes subjected to autoradiography and were assessed for arachidonic acid metabolism. Arachidonic acid had not been overtly metabolized nor oxygenated, and thus, radioactivity represented arachidonic acid. The capacity for arachidonic acid uptake was dependent primarily on megakaryocyte cytoplasmic maturation as judged by morphologic stage. Stage I and II megakaryocytes, immature cells, took up three times more arachidonic acid than stage III megakaryocytes and four times more than stage IV megakaryocytes, mature megakaryocytes, when calculated as uptake per cell. When uptake was calculated per megakaryocyte area, an approximation of megakaryocyte volume, arachidonic acid uptake was six times greater in stage I and II than in stage III and IV megakaryocytes. Arachidonic acid uptake was related to ploidy to a lesser extent, because 8N megakaryocytes took up two times more arachidonic acid than 32N megakaryocytes when calculated as uptake per cell area. Arachidonic acid uptake was independent of megakaryocyte size when assessed within each morphologic stage group and ploidy class.(ABSTRACT TRUNCATED AT 250 WORDS)