title: Three conductance classes of nicotinic acetylcholine receptors are expressed in developing amphibian skeletal muscle.
abstract: Two previously described classes of nicotinic AChRs in vertebrate skeletal muscle have conductances of 40 and 60 pS. In addition, a third conductance class of AChR channels is present in developing Xenopus muscle. This class appears to represent an independent channel type, rather than a subconductance state of the larger conductance channels. The channel has a slope conductance of 25 pS and a reversal potential of about 0 mV membrane potential. Its kinetic properties resemble those of the 40 pS channels present in early embryonic myotomal muscle. The channel has a mean open time of about 6 msec (at 40 mV applied potential). The open time is dependent on membrane potential and increases e-fold for every 60 mV of hyperpolarization. Consecutive openings were often separated by brief closures of about 0.4 msec in duration. The identity of the channel as a nicotinic AChR was established by blocking the channel openings with alpha-BTX and by demonstrating bursting and desensitization in the presence of high agonist concentrations. In some muscles (e.g., extraocular), this channel may be a predominant form at early developmental stages and could therefore be important to the function of developing synapses in those muscles.
authors.affiliation: Biology Department, University of Alaska, Anchorage 99508.
authors.forename: J L
authors.initials: JL
authors.lastname: Owens
authors.forename: R
authors.initials: R
authors.lastname: Kullberg
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002038:Bungarotoxins / Q000494:pharmacology; D004553:Electric Conductivity; D004594:Electrophysiology; D007700:Kinetics; D024510:Muscle Development; D009132:Muscles / Q000378:metabolism*; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000502:physiology*; D014982:Xenopus laevis / Q000254:growth & development / Q000378:metabolism*
chemical_list: D002038:Bungarotoxins; D011978:Receptors, Nicotinic