[3H]desipramine binding to rat brain tissue: binding to both noradrenaline uptake sites and sites not related to noradrenaline neurons.
The pharmacological and biochemical characteristics of [3H]desipramine binding to rat brain tissue were investigated. Competition studies with noradrenaline, nisoxetine, nortriptyline, and desipramine suggested the presence of more than one [3H]desipramine binding site. Most of the noradrenaline-sensitive binding represented a high-affinity site, and this site appeared to be the same as the high-affinity site of nisoxetine-sensitive binding. The [3H]desipramine binding sites were abolished by protease treatment, a result suggesting that the binding sites are protein in nature. When specific binding was defined by 0.1 microM nisoxetine, the binding was saturable and fitted a single-site binding model with a binding affinity of approximately 1 nM. This binding fraction was abolished by lesioning of the noradrenaline neurons with the noradrenaline neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4). In contrast, when 10 microM nisoxetine was used to define the specific binding, the binding was not saturable over the nanomolar range, but the binding fitted a two-site binding model with KD values of 0.5 and greater than 100 nM for the high- and low-affinity components, respectively. The high-affinity site was abolished after DSP4 lesioning, whereas the low-affinity site remained. The binding capacity (Bmax) for binding defined by 0.1 microM nisoxetine varied between brain regions, with very low density in the striatum (Bmax not possible to determine), 60-90 fmol/mg of protein in cortical areas and cerebellum, and 120 fmol/mg of protein in the hypothalamus. The binding capacities of these high-affinity sites correlated significantly with the regional distribution of [3H]noradrenaline uptake but not with 5-[3H]hydroxytryptamine uptake.(ABSTRACT TRUNCATED AT 250 WORDS)
Bäckström
I T
IT
Department of Geriatric Medicine, University of Umeå, Sweden.
Ross
S B
SB
Marcusson
J O
JO
D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D001921:Brain / Q000166:cytology / Q000378:metabolism*; D003891:Desipramine / Q000378:metabolism*; D010450:Endopeptidases / Q000494:pharmacology; D005473:Fluoxetine / Q000031:analogs & derivatives / Q000494:pharmacology; D008297:Male; D009474:Neurons / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D014018:Tissue Distribution; D014316:Tritium
D005473:Fluoxetine; D014316:Tritium; C011386:nisoxetine; D010450:Endopeptidases; D003891:Desipramine; D009638:Norepinephrine