Abstract
We investigated the binding characteristics of 125I-(−)-m-iodovesamicol (125I- (−)-mIV), radioiodinated at the meta position of the 4-phenylpiperidine moiety, in cerebral membranes of the rat brain. The receptor binding affinity of (−)-mIV (Ki = 37 nM) was comparable to that of (−)-vesamicol (Ki = 30 nM). The stereoselectivity of (−)-mIV and (−)-vesamicol for the vesamicol receptor was very high [ both (−)mIY and (−)-vesamicol binding more than 20-fold more active than their (+)isomers], and 125I-(−)-mIV had low affinity for the sigma, dopamine, serotonin, adrenaline and acetylcholine receptors. Furthermore, in a saturation binding study using cerebral membrane preparations, (−)-mIV exhibited a Kd of 18.2 nM with maximum number of binding site Bmax of 660 fmol/mg of protein. These results showed that the characteristics of binding between (−)-mIV and (−)-vesamicol to cholinergic binding sites in the rat brain were similar.
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