Spontaneous and agonist-induced openings of an acetylcholine receptor channel composed of bovine muscle alpha-, beta- and delta-subunits.
During the development of mammalian muscle the gamma-subunit of the nicotinic acetylcholine receptor (AChR) is replaced by the epsilon-subunit to produce well-defined alterations in the conductance and gating of the channel. To gain a better understanding of the functional role of the gamma- and epsilon-subunits, we have studied the properties of an AChR channel lacking these subunits. The AChR expressed in Xenopus oocytes injected with the bovine alpha-, beta- and delta-subunit-specific mRNAs (referred to as alpha beta delta-AChR) is unusual in that its channel opens spontaneously at a high frequency in the absence of agonist. From a comparison of the alpha beta delta-AChR with complete receptors containing either the gamma- or epsilon-subunit, we conclude that the gamma- and epsilon-subunits influence most channel properties, including agonist binding, and are especially important for stabilizing the closed state of the unliganded receptor channel. The alpha beta delta-AChR can form when a complete set of four subunit-specific mRNAs is injected. The ease with which it is assembled raises the possibility that the alpha beta delta-AChR contributes to some of the variations in receptor properties that occur during development.
Jackson
M B
MB
Department of Physiology, University of Wisconsin, Madison 53706.
Imoto
K
K
Mishina
M
M
Konno
T
T
Numa
S
S
Sakmann
B
B
D000818:Animals; D002417:Cattle; D004594:Electrophysiology; D066298:In Vitro Techniques; D007473:Ion Channels / Q000378:metabolism; D007700:Kinetics; D008564:Membrane Potentials / Q000502:physiology; D009132:Muscles / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011950:Receptors, Cholinergic / Q000378:metabolism*; D014982:Xenopus laevis
D007473:Ion Channels; D012333:RNA, Messenger; D011950:Receptors, Cholinergic