PHARMACOLOGY OF SUCCINYLCHOLINE

Structure-Activity Relationships

All neuromuscular blockers are structurally related to acetylcholine. Neuromuscular blocking agents are quaternary ammonium compounds. Positive charges at these sites in the molecules mimic the quaternary nitrogen atom of the transmitter acetylcholine and are the principal reason for the attraction of these drugs to cholinergic nicotinic receptors at the neuromuscular junction. These receptors are also located at other physiologic sites of acetylcholine in the body, such as the nicotinic receptors in autonomic ganglia and as many as five different muscarinic receptors on both the parasympathetic and sympathetic sides of the autonomic nervous system. In addition, populations of nicotinic and muscarinic receptors are located prejunctionally at the neuromuscular junction.^[27]

The depolarizing neuromuscular blocker succinylcholine is composed of two molecules of acetylcholine linked back to back through the acetate methyl groups ( Fig. 13-5 ). As described by Bovet,^[61] succinylcholine is a long, thin, flexible molecule. Like acetylcholine, succinylcholine stimulates cholinergic receptors at the neuromuscular junction and at nicotinic (ganglionic) and muscarinic autonomic sites to open the ionic channel in the acetylcholine receptor.