REGIONAL DIFFERENCES IN H3-NOREPINEPHRINE AND H3-DOPAMINE UPTAKE INTO RAT BRAIN HOMOGENATES

Abstract

The uptake of DL-H 3 -norepinephrine and H 3 -dopamine has been examined in rat brain homogenates. The greatest amine accumulation by particulate fractions isolated from these homogenates occurred when brains were homogenized in sucrose and incubated with Krebs-Henseleit solution. At amine concentrations ranging from 0.05 µM to 0.80 µM, catecholamine uptake was saturable in all six brain areas examined. H 3 -dopamine accumulation exceeded that of H 3 -norepinephrine at all amino concentrations. In the cerebellum, medulla oblongata-pons, midbrain, cerebral cortex and hypothalamus, the K m for H 3 -norepinephrine uptake was 4.0 x 10 -7 M. In the striatum the K m for H 3 -norepinephrine uptake was 2.0 x 10 -6 M, whereas the K m for H 3 -dopamine uptake in this area was 4.0 x 10 -7 M. The K 1 values for the mutual competitive inhibition of the uptake of norepinephrine and dopamine in the striatum were the same as their K m values. In areas outside the striatum, H 3 -dopamine was accumulated by two uptake systems, with K m values of 0.8 x 10 -7 M (uptake a) and 1.4 x 10 -6 (uptake b), respectively. The K 1 for the inhibition of H 3 -norepinephrine uptake in the cerebral cortex by dopamine was identical with the K m for uptake a, indicating that this high-affinity uptake for dopamine appears to utilize the norepinephrine transport system.