The epsilon subunit confers fast channel gating on multiple classes of acetylcholine receptors

During vertebrate skeletal muscle development, multiple forms of long-open-time (slow-type) ACh receptor channels are replaced by at least two different types of short-opentime (fast-type) ACh receptors. Expression of ACh receptors in Xenopus oocytes indicates that the substitution of an ε subunit for a γ subunit may account for both types of fastgated channel types in adult muscle. Unlike the various forms of the embryonic receptor, in which functional diversity is achieved through alterations in subunit composition, the two major fast-gated forms expressed in oocytes have identical subunit composition. These findings provide a structural basis for both types of short-open-time ACh receptor types found in adult muscle.