Binding characteristics of [3H]DAA1106, a novel and selective ligand for peripheral benzodiazepine receptors.
Here, we investigated the binding characteristics of [3H]N-(2,5-dimethoxybenzyl)-N-(5-fluoro-2-phenoxyphenyl)acetamide ([3H]DAA1106), a potent and selective ligand for peripheral benzodiazepine receptors, in mitochondrial fractions of the rat brain. [3H]DAA1106 bound to the mitochondrial fraction of the rat brain in a saturable manner. The dissociation constant (Kd) and maximal number of binding sites (Bmax) obtained from Scatchard plot analysis of the saturation curve of [3H]DAA1106 binding were 0.12 +/- 0.03 nM and 161.03 +/- 5.80 fmol/mg protein, respectively. [3H]DAA1106 binding to mitochondrial preparations of the rat cerebral cortex was inhibited by several peripheral benzodiapine receptor ligands, and DAA1106 was the most potent inhibitor in inhibiting [3H]DAA1106 binding among the peripheral benzodiazepine receptor ligands we tested. The binding of [3H]DAA1106 was not affected by several neurotransmitter-related compounds, including adrenoceptor, gamma-aminobutyric acid (GABA), dopamine, 5-hydroxytryptamine (5-HT), acetylcholine, histamine, glutamate and central benzodiazepine receptor ligands even at a concentration of 10 microM. In the cerebral cortex of rhesus monkeys, DAA1106 and 1-(2-chlorophenyl)-N-methyl-(1-methylpropyl)-3-isoquinoline carboxamide (PK11195) potently inhibited [3H]DAA1106 binding, while 7-chloro-5-(4-chlorophenyl)-1-methyl-1,3-dihydrobenzo[e][1,4]diazepin -2-one (Ro5-4864) did not. The highest [3H]DAA1106 binding was observed in the olfactory bulb, followed by the cerebellum. In autoradiographic studies, practically the same results were obtained, in that the highest binding of [3H]DAA1106 was in the olfactory bulb. Potent labeling was also noted in ventricular structures such as the choroid plexus. Thus, [3H]DAA1106 is a potent and selective ligand for peripheral benzodiazepine receptors and should prove useful for elucidating the physiological relevance of events mediated through peripheral benzodiazepine receptors.
Chaki
S
S
1st Laboratory, Medicinal Research Laboratories, Taisho Pharmaceutical, Ohmiya, Saitama, Japan. S13555@ccm.taisho.co.jp
Funakoshi
T
T
Yoshikawa
R
R
Okuyama
S
S
Okubo
T
T
Nakazato
A
A
Nagamine
M
M
Tomisawa
K
K
D000081:Acetamides / Q000378:metabolism*; D000818:Animals; D014151:Anti-Anxiety Agents / Q000378:metabolism*; D001345:Autoradiography; D001665:Binding Sites; D001921:Brain / Q000378:metabolism*; D002531:Cerebellum / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism; D004347:Drug Interactions; D066298:In Vitro Techniques; D008024:Ligands; D008253:Macaca mulatta; D008297:Male; D008928:Mitochondria / Q000378:metabolism*; D018377:Neurotransmitter Agents / Q000378:metabolism; D009830:Olfactory Bulb / Q000378:metabolism; D010647:Phenyl Ethers / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D011963:Receptors, GABA-A / Q000378:metabolism*
D000081:Acetamides; D014151:Anti-Anxiety Agents; C118942:DAA 1106; D008024:Ligands; D018377:Neurotransmitter Agents; D010647:Phenyl Ethers; D011963:Receptors, GABA-A