Journal of Neuroscience, Vol 5, 1917-1924, Copyright © 1985 by Society for Neuroscience
The effects of a myasthenic serum on the acetylcholine receptors of C2 myotubes. II. Functional inactivation of the receptor
AV Maricq, Y Gu, S Hestrin and Z Hall
We have investigated the effect of antibodies from a myasthenic serum on
the physiological properties of acetylcholine receptors (AChRs) in myotubes
of a mouse muscle cell line, C2. The antibodies in this serum blocked the
binding of 125I-alpha-bungarotoxin to the myotubes to an extent of about
50%. The antibodies also inhibited the increase in 22Na influx caused by
carbamylcholine (CARB). At a concentration of antibody that blocked about
50% of toxin binding, greater than 80% of the AChR- mediated 22Na influx
was blocked. The apparent KD for CARB, estimated from the dose-response
curve for 22Na influx, was unaffected. The effect of the antibodies was
further examined by patch-clamp recording. In greater than 30% of the
patches from antibody-treated cells, no channel activity in response to
acetylcholine was seen; in contrast, every patch from control cells showed
activity. The channels that were seen after antibody treatment were
indistinguishable from those seen in normal cells, both in their
single-channel conductance and in the kinetic constants used to describe
channel opening and closing. We conclude that the antibodies in this serum
inhibit the functional response of AChRs in C2 myotubes to acetylcholine
and do so by inactivating individual receptors.