Figure 1.

Outline of muscle acetylcholine receptor channels (right) and tracings of cell patch records of receptor channel openings (left). The acetylcholine receptor consists of five subunits. The mature receptor consists of two α1 subunits, and one each of β1, δ, and ε subunits. The immature isoform consists of two α1 subunits and one β1, δ, and γ subunit. The five subunits form a transmembrane cation channel. The immature receptor shows long opening times and low-amplitude currents and is therefore considered a low conductance channel. It may be depolarized with lower concentrations of agonists. The fact that these immature channels remain open for longer and are upregulated in certain pathologic states increases the chance that intracellular potassium ions will leak to the extracellular space following activation of the acetylcholine receptor with suxamethonium, acetylcholine, or choline and illustrated with permission from Wolters Kluwer [4].