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-open-time (fast-type) ACh receptors. Expression of ACh receptors in Xenopus oocytes indicates that the substitution of an epsilon subunit for a gamma subunit may account for both types of fast-gated 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.