Cholinergic sites in skeletal muscle. II. Interaction of an agonist and two antagonists with the acetylcholine site.
The equilibrium interactions of alpha-bungarotoxin, d-tubocurarine, and carbamylcholine with junctional and extrajunctional skeletal muscle acetylcholine receptors were examined. d-Tubocurarine is a competitive inhibitor of the bindings of alpha-bungarotoxin to the acetylcholine receptor. No substantive difference was observed in the association of d-tubocurarine with the junctional and extrajunctional receptors. In contrast, the carbamylcholine inhibition of toxin binding is not competitive. The data indicate that either the single set of alpha-bungarotoxin and d-tubocurarine bindings sites contains two subsets of carbamylcholine sites or that the carbamylcholine binds in a cooperative manner to a single set of sites. In addition, the affinity of carbamylcholine for extrajunctional receptors may be higher than the affinity for junctional receptors.
D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002038:Bungarotoxins / Q000378:metabolism*; D002217:Carbachol / Q000378:metabolism*; D005260:Female; D009121:Muscle Denervation; D009132:Muscles / Q000378:metabolism*; D051381:Rats; D011950:Receptors, Cholinergic / Q000187:drug effects*; D014403:Tubocurarine / Q000378:metabolism*
D002038:Bungarotoxins; D011950:Receptors, Cholinergic; D002217:Carbachol; D000109:Acetylcholine; D014403:Tubocurarine