TUNICAMYCIN ALTERS CHANNEL GATING CHARACTERISTICS OF JUNCTIONAL AND EXTRAJUNCTIONAL ACETYLCHOLINE-RECEPTORS EXPRESSED IN XENOPUS-OOCYTES

The acute effects of tunicamycin on mouse junctional and extrajunction al acetylcholine receptors (AChRs) expressed in Xenopus oocytes, disti nct from its ability to block N-glycosylation of the protein, was exam ined at the single channel level. Tunicamycin reduced the frequency of ACh-activated single channel openings and prolonged the mean channel open times of AChRs in a dose-dependent manner, without affecting inwa rd conductances. Continuous application of ACh to both junctional and extrajunctional AChR channels very slowly decreased the number of chan nel opening events, and tunicamycin accelerated this process. These re sults suggest that tunicamycin alters channel gating kinetics and acce lerates transition towards a desensitized state.