The influence of guanyl-5′-yl imidodiphosphate and sodium chloride on the binding of the muscarinic agonist, [3H] cis methyldioxolane

[³H]Quinuclydinyl benzylate([³H]QNB) binding was carried out on crude synaptosomal membranes isolated from cat cerebral cortex. The specific binding showed a single type of site with K_D 0.25 nM, Hill number 0.89 and B_max 114 pmol/g protein. The local anesthetics procaine, tetracaine, and the adrenergic antagonists phentolamine and propranolol, in concentrations between 1 nM and 500 μM, inhibited [³H]QNB binding with K_i varying between 9 μM for procaine and 80 μM for propranolol. The Hill coefficients obtained from logit/log plots suggested that there was no cooperativity between the binding sites for local anesthetics. At various concentrations the inhibition by procaine and propranolol may appear as competitive or non-competitive. The Hill numbers obtained from the saturation curves suggest that there was no cooperativity between anesthetics and [³H]QNB binding sites. Neither 1 mM Ca²⁺ nor Mg²⁺ affected [³H]QNB binding or the action of the drugs. The effect of local anesthetics and adrenergic antagonists was reversible and these drugs did not protect the muscarinic receptor from the deleterious effect of Triton X-100 as was the case with muscarinic agents. Our findings suggest that local anesthetics inhibit [³H]QNB binding to the muscarinic receptor by acting at some accessory site but not on the true receptor site. The possible mechanism of action of local anesthetics on synaptic transmission is discussed.