Single Amino Acid Residue in the Extracellular Portion of Transmembrane Segment 2 in the Nicotinic α7 Acetylcholine Receptor Modulates Sensitivity to Ketamine

Background: Ketamine inhibits the activation of both heteromeric and homomeric nicotinic acetylcholine receptors. The site of molecular interaction is unknown.

Methods: The inhibition of [alpha]7 nicotinic acetylcholine receptors by ketamine was compared to that of 5-hydroxytryptamine-3A (5HT3A)receptors that are resistant to ketamine inhibition in Xenopus laevis oocytes. To determine whether the region of transmembrane segments 2 and 3 is relevant for ketamine inhibition of nicotinic receptors, the authors identified single amino acid residues that differ in the sequence alignment of the two proteins. They created 22 mutant [alpha]7 nicotinic receptors that contain the single homologous amino acid residue in the 5HT3A sequence.

Results: Of the 22 mutant [alpha]7 nicotinic receptors tested, only one ([alpha]7 A258S) was significantly resistant to 20 [mu]m ketamine. The ketamine concentration response relationship for the [alpha]7 A258S mutant was shifted to the right with the IC50 for ketamine increased from 17 +/- 2 for wild type to 30 +/- 3 [mu]m in the mutant (P < 0.001). Agonist activation was unchanged by the mutation. The homologous amino acid residue in the 5HT3A receptor was mutated to the alanine that occurs in the wild-type nicotinic receptor. This mutation made the previously insensitive 5HT3A receptor sensitive to ketamine (P < 0.001).