Genetic variants of C2 muscle cells that are defective in synthesis of the alpha-subunit of the acetylcholine receptor.
We have analyzed two genetic variants of C2 muscle cells that have reduced levels of binding activity for alpha-bungarotoxin and have found that both synthesize only low levels of the alpha-subunit of the acetylcholine receptor. In both variants the uptake of 22Na in response to carbachol is diminished in proportion to the reduction in toxin-binding activity. In addition, the kinetic and sedimentation properties of the residual toxin-binding activity in both is indistinguishable from that seen in wild-type cells. Immunoblotting experiments on extracts of the variants using subunit-specific antibodies to alpha- and beta-subunits of the acetylcholine receptor demonstrated that the beta-subunit was present, but failed to detect alpha-subunit. In both variants, the amount of alpha-subunit accumulated after a 5-min period of labeling with [35S]methionine was reduced by over 90%, leading to the conclusion that the alpha-subunit is synthesized at greatly reduced rates. Northern blot and S1 nuclease analysis showed no differences between the alpha-subunit mRNA in wild-type and variant cells.
Black
R
R
Salk Institute, Biological Studies, San Diego, California 94305.
Goldman
D
D
Hochschwender
S
S
Lindstrom
J
J
Hall
Z W
ZW
D000818:Animals; D000911:Antibodies, Monoclonal; D002038:Bungarotoxins / Q000378:metabolism; D002460:Cell Line; D014644:Genetic Variation; D007700:Kinetics; D046911:Macromolecular Substances; D009132:Muscles / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D011950:Receptors, Cholinergic / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism
D000911:Antibodies, Monoclonal; D002038:Bungarotoxins; D046911:Macromolecular Substances; D012333:RNA, Messenger; D011950:Receptors, Cholinergic