Desensitization of junctional and extrajunctional nicotinic ACh receptors expressed in Xenopus oocytes.

Desensitization of nicotinic acetylcholine receptors (AChRs) was studied using the Xenopus oocyte expression system. Mouse and cat extrajunctional AChRs expressed in oocytes desensitized more slowly than Torpedo AChRs. Substitution of the mouse gamma subunit into the Torpedo AChR reduced the rate of desensitization, making it similar to the mouse AChR. Likewise, substitution of the Torpedo gamma subunit into the mouse extrajunctional AChR increased the rate of desensitization, making it similar to the Torpedo AChR. Furthermore, mouse junctional AChRs in which the gamma subunit was replaced by the epsilon subunit desensitized more rapidly than either mouse or cat extrajunctional AChRs, and resembled Torpedo AChRs. Thus, in addition to other properties, junctional and extrajunctional AChRs differ with respect to desensitization, suggesting a possible role of desensitization in normal development of neuromuscular junction.