IgG from amyotrophic lateral sclerosis affects tubular calcium channels of skeletal muscle

Amyotrophic lateral sclerosis (ALS) is a devastating human disease of upper and lower motoneurons. We studied the action of the immunoglobulin G (IgG) from ALS and disease control patients on dihydropyridine (DHP)-sensitive Ca²⁺ channels in single mammalian skeletal muscle fibers with the double Vaseline gap technique. The peak of the Ca²⁺ current (I(Ca)) and the charge movement were reduced when the fibers were incubated in ALS IgG. These effects were lost when the IgG was boiled or adsorbed with skeletal tubular membranes. ALS IgG reduced skeletal muscle I(Ca) in a similar fashion as nifedipine; the I(Ca) blockade was voltage dependent, and the associated charge movement was reduced. These observations suggest that IgG from ALS patients reacts with the skeletal muscle DHP-sensitive Ca²⁺ channels or some associated regulatory moiety.