Subunit requirements for Torpedo AChR channel expression: a specific role for the delta-subunit in voltage-dependent gating.

This study examines the subunit requirement for Torpedo acetylcholine receptor (AChR) channel expression and the influence of non-alpha-subunit deletions on single AChR-channel currents. Xenopus oocytes injected with subunit combinations deficient in single non-alpha-subunit mRNA transcripts display the following order of ACh sensitivity: beta-less > gamma-less > delta-less. Oocytes injected with only the alpha-subunit and one non-alpha-subunit display the order: alpha delta > alpha gamma > alpha beta. These sequences indicate the effectiveness of non-alpha-subunit substitution is delta > gamma > beta. Single AChR-channel currents measured in oocytes deficient in either beta or gamma display conductance and voltage-sensitive burst kinetics similar to the wild-type channel. In contrast, the delta-less combination express channels with burst kinetics that are relatively faster and voltage insensitive. These results indicate that either a specific structural domain in the delta-subunit or its specific interactions with the alpha-subunit contribute to the voltage-dependent gating of the Torpedo AChR channel.