Muscarinic Cholinergic Binding in Rat Brain

TLDR

Binding sites with high affinity and specificity for [3H]QNB are present in rat brain homogenates and resemble muscarinic cholinergic receptors. Specific [3H]QNB binding in rat brain is saturable, time‑, temperature‑, and pH‑dependent, has a dissociation constant of 60 pM and a density of 65 pmol/g, and is displaced by muscarinic agonists and antagonists but not by nicotinic or non‑cholinergic drugs.

Abstract

Binding sites with high affinity and specificity for [ 3 H]quinuclidinyl benzilate (QNB) are present in homogenates of rat brain. The characteristics of the binding sites resemble those of muscarinic cholinergic receptors. Specific binding is saturable with respect to [ 3 H]QNB and tissue concentration and is time-, temperature-, and pH-dependent. The bimolecular rate of association (2.0 × 10 8 M -1 min -1 ) and dissociation (1.2 × 10 -2 min -1 ) at 35° indicate a dissociation constant of 60 pM and a density of 65 pmol/g of brain. Muscarinic antagonists and agonists displace specific [ 3 H]QNB binding, while nicotinic and non-cholinergic drugs possess little affinity for [ 3 H]QNB-binding sites.