The action of Lambert-Eaton myasthenic syndrome immunoglobulin G on cloned human voltage-gated calcium channels.
In the Lambert-Eaton myasthenic syndrome (LEMS), immunoglobulin G (IgG) autoantibodies to presynaptic voltage-gated calcium channels (VGCCs) at the neuromuscular junction lead to a reduction in nerve-evoked release of neurotransmitter and muscle weakness. We have examined the action of LEMS IgGs on cloned human VGCCs stably expressed in transfected human embryonic kidney (HEK293) cell lines: 10-13 (alpha(1A-2), alpha(2b)delta, beta(4a)) and C2D7 (alpha(1B-1), alpha(2b)delta, beta(1b)). All LEMS IgGs studied showed surface binding to [(125)I]-omega-CTx-MVIIC-labeled VGCCs in the alpha(1A) cell line and two of six IgGs showed surface binding to [(125)I]-omega-CTx-GVIA-labeled VGCCs in the alpha(1B) cell line. We next studied the effect of LEMS IgGs (2 mg/ml) on whole-cell calcium currents in the alpha(1A) and alpha(1B) cell lines. Overnight treatment of alpha(1A) (10-13) cells with LEMS IgGs led to a significant reduction in peak current density without alteration of the current-voltage relationship or the voltage dependence of steady-state inactivation. In contrast, LEMS IgGs did not reduce peak current density in the alpha(1B) cell line. Overall these data demonstrate the specificity of LEMS IgGs for the alpha(1A) cell line and suggest that LEMS IgGs bind to and downregulate VGCCs in this cell line. Although several LEMS IgGs can be shown to bind to the alpha(1B) (C2D7) cell line, no functional effects were seen on this channel.
Pinto
Ashwin
A
Neurosciences Group, Institute of Molecular Medicine, Oxford University, John Radcliffe Hospital, Headington, Oxford OX3 9DS, UK.
Iwasa
Kazuo
K
Neurosciences Group, Institute of Molecular Medicine, Oxford University, John Radcliffe Hospital, Headington, Oxford OX3 9DS, UK.|Department of Neurology, Kanazawa University School of Medicine, Kanazawa, Japan.
Newland
Claire
C
Neurosciences Group, Institute of Molecular Medicine, Oxford University, John Radcliffe Hospital, Headington, Oxford OX3 9DS, UK.
Newsom-Davis
John
J
Neurosciences Group, Institute of Molecular Medicine, Oxford University, John Radcliffe Hospital, Headington, Oxford OX3 9DS, UK.
Lang
Bethan
B
Neurosciences Group, Institute of Molecular Medicine, Oxford University, John Radcliffe Hospital, Headington, Oxford OX3 9DS, UK.
D001464:Barium / Q000502:physiology; D002121:Calcium Channel Blockers / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects* / Q000235:genetics* / Q000502:physiology; D002460:Cell Line; D003001:Cloning, Molecular; D004553:Electric Conductivity; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood* / Q000494:pharmacology*; D015624:Lambert-Eaton Myasthenic Syndrome / Q000097:blood*; D018408:Patch-Clamp Techniques; D011233:Precipitin Tests; D013696:Temperature; D020866:omega-Conotoxin GVIA / Q000378:metabolism; D020960:omega-Conotoxins / Q000378:metabolism
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D007074:Immunoglobulin G; D020960:omega-Conotoxins; C075851:omega-conotoxin-MVIIC; D001464:Barium; D020866:omega-Conotoxin GVIA