Serotonin uptake, storage and metabolism in megakaryoblasts

Serotonin (5-hydroxytryptamine, 5-HT) uptake, storage and metabolism in human megakaryoblastic cell line (Meg-01) which acts as a model for megakaryocyte precursors, megakaryoblasts were investigated by using biochemical (HPLC) and morphological (electron microscope, EM) techniques. Results showed that Meg-01 cells were able to take up 5-HT. The intracellular 5-HT level was 2.8 +/- 0.4 and 51.8 +/- 4.9 (1 h) or 59.0 +/- 4.4 (2 h) ng/10(6) cells, before and after incubation with 5-HT, respectively, but no dense bodies were visualized after incubation with excess 5-HT by electron microscope observation. This uptake was inhibited by 28% on pre-incubation with fluoxetine and 60% of 5-HT in the cells was released on incubation with reserpine. 5-Hydroxyindoleacetic acid (5-HIAA) concentration of Meg-01 cells was increased after incubation of the cells with 5-HT (0 and 17.6 +/- 2.1 or 19.9 +/- 1.9 ng/10(6) cells, before and after incubation 1 or 2 h, respectively). The study suggests that: (1) 5-HT uptake ability is well established in megakaryocytes precursors, megakaryoblasts and the uptake ability is affected by reserpine and fluoxetine; (2) however, the capacity to store the amine is not well developed in megakaryoblasts and (3) megakaryoblasts may contain monoamine oxidase (MAO) which converts 5-HT to 5-HIAA.