Subunit requirements for Torpedo AChR channel expression: A specific role for the δ-subunit in voltage-dependent gating

This study examines the subunit requirement for Torpedo acetylcholine receptor (AChR) channel expression and the influence of non-α-subunit deletions on single AChR-channel currents. Xenopus oocytes injected with subunit combinations deficient in single non-α-subunit mRNA transcripts display the following order of ACh sensitivity: β-less > γ-less > δ-less. Oocytes injected with only the α-subunit and one non-α-subunit display the order: αδ > αγ > αβ. These sequences indicate the effectiveness of non-α-subunit substitution is δ > γ > β. Single AChR-channel currents measured in oocytes deficient in either β or γ display conductance and voltage-sensitive burst kinetics similar to the wild-type channel. In contrast, the δ-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 δ-subunit or its specific interactions with the α-subunit contribute to the voltage-dependent gating of the Torpedo AChR channel.