High- and low-affinity binding of [3H]acetylcholine at nicotinic cholinergic receptors in rat brain.

There is both high-affinity and low-affinity nicotinic cholinergic binding of [3H]acetylcholine [( 3H]ACh) in rat brain membrane preparations. As determined by a filtration binding assay, [3H]ACh bound with Kd = 36.0 +/- 8.4 nM and Bmax = 19.4 +/- 4.5 fmol/mg protein or 3.3 +/- 0.7 fmol/mg tissue for high-affinity binding and Kd about 10(-7) to 10(-6) M and Bmax about 6-10 fmol/mg tissue or 40-60 fmol/mg protein for low-affinity binding. d-Tubocurarine (1 mM) inhibits high- as well as low-affinity binding, whereas 10 microM alpha-bungarotoxin does not compete at both binding sites. Substance P had no effect on the binding parameters of high-affinity nicotinic cholinergic binding.