Subcellular fractionation of striatum: sedimentation properties of dopaminergic synaptosomes.

Linear sucrose density gradient centrifugation of a crude synaptosomal-mitochondrial preparation of rat striatum was performed at 82,500g for 7.5, 15 and 30 min and 1, 4 and 20 h. After centrifugation various marker enzyme activities were measured throughout the gradients, viz. tyrosine hydroxylase (TH) and DOPA decarboxylase (DD) as markers of dopaminergic synaptosomes, lactate dehydrogenase (LDH) as a general synaptosomal marker and monoamine oxidase (MAO) as a mitochondrial marker. At all centrifugation times the distribution patterns of TH and DD activity coincided almost perfectly. Notable differences were found between the sedimentation properties of these TH/DD-containing particles and LDH-containing particles: TH and DD were symmetrically distributed in the gradient much sooner than LDH, at all centrifugation times the top of the TH and DD curves was lying deeper in the gradient than the highest LDH activity, and TH and DD became enriched in the gradients to a much greater extent than LDH. It is concluded that rat striatal dopaminergic synaptosomes form a relatively homogeneous population of particles sedimenting faster into the gradients than the bulk of striatal synaptosomes does. This distinct sedimentation behaviour of the dopaminergic synaptosomes can be usefully applied for analytical purposes.