Histidine Transport into Rat Brain Synaptosomes

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Abstract
Histidine transport and metabolism in rat brain synaptosomes were investigated to study the possible role of histidine uptake in the synthesis of the putative neurotransmitter histamine (HA). Histidine uptake was found to be regionally distributed and temperature sensitive and was not totally independent of Na or K ions. Transport was inhibited by metabolic inhibitors and by promethazine and quinacrine. A number of other HA-related agents and several histidine metabolites had no effect. Kinetic analyses of histidine transport revealed the presence of high- and low-affinity systems in cerebral cortex. Histidine uptake increased following preexposure of synaptosomes to depolarizing concentrations of K. This effect was dependent on the presence of Ca ions during the preincubation. No newly formed [3H]HA was detectable in rat brain synaptosomes following [3H]histidine transport. Lesions of the medial forebrain bundle did not alter histidine uptake in the hippocampus or cerebral cortex. Ontogenic studies indicated that the histidine uptake system developed rapidly and reached a peak during postnatal days 12-17. These findings do not support a role for histidine transport in the regulation or maintenance of neurotransmitter pools of HA in rat brain.