The action of amyotrophic lateral sclerosis immunoglobulins on mammalian single skeletal muscle Ca2+ channels.
1. The planar phospholipid bilayer technique was used to study the T-tubule skeletal muscle dihydropyridine (DHP)-sensitive calcium (Ca2+) channel. To improve the signal-to-noise ratio, Ca2+ channel activity was recorded using both 800-50 and 500-50 mM NaCl gradients. 2. Ca2+ channels were characterized by their cation selectivity and pharmacological profile. The mean open time for channels identified by these techniques was increased by the DHP agonist Bay K 8644 (2 microM), while it was decreased by the DHP antagonist nifedipine (5 microM). Nifedipine also reduced Ca2+ channel amplitude levels. 3. Immunoglobulins G (IgG) from three amyotrophic lateral sclerosis (ALS) patients (n = 14 experiments), one myasthenia gravis (MG) patient (n = 3 experiments) and one healthy individual (n = 4 experiments), were tested on Ca2+ channel activity at a final concentration of 3 mg/ml. 4. Channel mean open time, mean closed time and time integral for the current were not modified by normal IgG (n = 4 experiments). Similarly, MG IgG did not reduce channel activity (n = 3 experiments). 5. ALS IgG reduced the mean open time of DHP-sensitive Ca2+ channel activity in twelve out of fourteen experiments. In addition, in five out of twelve experiments, ALS IgG stabilized the channel to a smaller amplitude level. 6. ALS IgG reduced Ca2+ channel activity in a side-selective fashion, probably corresponding to the external side of the channel. 7. These results suggest that ALS IgG action on DHP-sensitive Ca2+ channels is not mediated by second messengers, thus favouring a direct mechanism for interaction with the DHP receptor complex.
Magnelli
V
V
Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX 77030.
Sawada
T
T
Delbono
O
O
Smith
R G
RG
Appel
S H
SH
Stefani
E
E
D000690:Amyotrophic Lateral Sclerosis / Q000276:immunology*; D015220:Calcium Channels / Q000187:drug effects / Q000276:immunology*; D004095:Dihydropyridines / Q000378:metabolism; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology*; D066298:In Vitro Techniques; D009132:Muscles / Q000276:immunology*; D009157:Myasthenia Gravis / Q000276:immunology; D009543:Nifedipine / Q000494:pharmacology
D015220:Calcium Channels; D004095:Dihydropyridines; D007074:Immunoglobulin G; D009543:Nifedipine