Protection by atropine of the inhibition caused by Triton X-100 on central muscarinic receptors.

Synaptosomal membranes from cat cerebral cortex were labelled with [3H]-quinuclidinyl benzylate ([3H]QNB). There was shown to be a single type of binding site with Kd = 0.34 nM, Bmax = 2.2 nmol/g protein and Hill No. = 1.01. Triton X-100 at 5 x 10(-4)% inhibited the specific binding of [3H]QNB and the inhibition was almost complete at 10(-2)%. Treatment with 2.5 x 10(-6) M atropine, followed by centrifugation washings protected the receptor site from the inhibitory action of the detergent. The protection afforded by other cholinergic drugs was less effective. The use of this technique has confirmed the results of our previous work on the possible pre- and postsynaptic location of central muscarinic receptors. These findings open the possibility for protection of other detergent-sensitive receptors and for their isolation and purification as well-defined macromolecules.