Adult forms of nicotinic acetylcholine receptors are expressed in the absence of nerve during differentiation of a mouse skeletal muscle cell line

Changes in the functional properties of acetylcholine receptor (AchR) channels were followed in the C2 muscle cell line over the period of 1 to 17 days following myotube formation. Up to 1 week after myotube formation, the predominant class of channel exhibited low (45 pS) conductance and long mean channel open time (14 msec), characteristic of the major type of AchR in embryonic skeletal muscle. Three additional Ach-activated currents with conductances lower than 45 pS and long channel open times were also observed. Seven to 10 days following myotube formation, channels of 45 pS and 65 pS and short (2-6 msec) mean open duration were observed, characteristic of receptor channels in adult muscle. Increases in ε subunit mRNA levels preceded the functional expression of channels with brief open durations. Our results show that C2 muscle cells maintained in culture express a full range of functionally distinct AchR types in the absence of nerve.