Uptake of 3H-dopamine in megakaryocytes and blood platelets measured by quantitative electron-microscope autoradiography

Summary We studied the uptake of dopamine by mature megakaryocytes and blood platelets in mouse spleen after a single intraperitoneal injection of ³H-dopamine. In order to compare the uptake of ³H-dopamine in mature megakaryocytes and blood platelets, we used quantitative autoradiography at the electron-microscope level. Dense accumulations of silver grains were observed on both mature megakaryocytes and blood platelets; all other tissue elements of the spleen exhibited considerably less dense labeling. No sigificant differences with regard to dopamine uptake were observed in megakaryocytes and blood platelets. This is in contrast to the previous finding of very different patterns of ³H-5-hydroxytryptamine labeling in mature megakaryocytes and blood platelets (Daimon and Uchida 1985). The results of the present study provide new evidence in favor of the hypothesis that the active uptake mechanism of dopamine through the plasma membrane is different from the uptake mechanism of 5-hydroxytryptamine.