Alcuronium: A non-depolarizing skeletal muscle relaxant similar to TUBOCURARINE. It is used as an anesthesia adjuvant.Toxiferine: A curare alkaloid that is a very potent competitive nicotinic antagonist at the neuromuscular junction.Gallamine Triethiodide: A synthetic nondepolarizing blocking drug. The actions of gallamine triethiodide are similar to those of TUBOCURARINE, but this agent blocks the cardiac vagus and may cause sinus tachycardia and, occasionally, hypertension and increased cardiac output. It should be used cautiously in patients at risk from increased heart rate but may be preferred for patients with bradycardia. (From AMA Drug Evaluations Annual, 1992, p198)N-Methylscopolamine: A muscarinic antagonist used to study binding characteristics of muscarinic cholinergic receptors.Parasympatholytics: Agents that inhibit the actions of the parasympathetic nervous system. The major group of drugs used therapeutically for this purpose is the MUSCARINIC ANTAGONISTS.Allosteric Regulation: The modification of the reactivity of ENZYMES by the binding of effectors to sites (ALLOSTERIC SITES) on the enzymes other than the substrate BINDING SITES.Receptors, Muscarinic: One of the two major classes of cholinergic receptors. Muscarinic receptors were originally defined by their preference for MUSCARINE over NICOTINE. There are several subtypes (usually M1, M2, M3....) that are characterized by their cellular actions, pharmacology, and molecular biology.