Zebrafish AChR subunit identification and functional expression in Xenopus oocytes. (A) A phylogenetic tree of AChR subunit genes constructed by the UPGMA method. Subunit sequences of human (Homo sapiens), mouse (Mus musculus), rat (Rattus norvegicus), puffer fish (Takifugu rubripes), and frog (Xenopus tropicalis) are included. Zebrafish genes are highlighted in red. (B) Two microelectrode recordings of membrane currents elicited by 30 µM ACh (bar) at a −80 mV holding potential. Shown are responses from oocytes expressing αβδε (red trace), αβδγ (green trace), or αβδ (blue trace) RNA. (C) The mean ± SD macroscopic current amplitude associated with the RNA subunit combinations is indicated. Xenopus αβδγ RNA is shown for comparison, and the number of oocytes tested is indicated for each RNA combination tested. The three combinations that yielded currents suitable for single-channel recordings are indicated by colored bars.