Stage V–VI Xenopus laevis oocytes were prepared as described previously (30 (link)). Oocytes injection and TEVC electrophysiological measurements were done as previously described (29 (link)). Amantadine (Sigma, St. Louis, MO) was applied to inhibit A/M2 induced currents. Data were analyzed using ORIGIN 8.0 software (OriginLab, Northampton, MA).