Calcium channel subtypes contributing to acetylcholine release from normal, 4-aminopyridine-treated and myasthenic syndrome auto-antibodies-affected neuromuscular junctions.
1 Acetylcholine release at the neuromuscular junction relies on rapid, local and transient calcium increase at presynaptic active zones, triggered by the ion influx through voltage-dependent calcium channels (VDCCs) clustered on the presynaptic membrane. Pharmacological investigation of the role of different VDCC subtypes (L-, N-, P/Q- and R-type) in spontaneous and evoked acetylcholine (ACh) release was carried out in adult mouse neuromuscular junctions (NMJs) under normal and pathological conditions. 2 omega-Agatoxin IVA (500 nM), a specific P/Q-type VDCC blocker, abolished end plate potentials (EPPs) in normal NMJs. However, when neurotransmitter release was potentiated by the presence of the K(+) channel blocker 4-aminopyridine (4-AP), an omega-agatoxin IVA- and omega-conotoxin MVIIC-resistant component was detected. This resistant component was only partially sensitive to 1 micro M omega-conotoxin GVIA (N-type VDCC blocker), but insensitive to any other known VDCC blockers. Spontaneous release was dependent only on P/Q-type VDCC in normal NMJs. However, in the presence of 4-AP, it relied on L-type VDCCs too. 3 ACh release from normal NMJs was compared with that of NMJs of mice passively injected with IgGs obtained from patients with Lambert-Eaton myasthenic syndrome (LEMS), a disorder characterized by a compromised neurotransmitter release. Differently from normal NMJs, in LEMS IgGs-treated NMJs an omega-agatoxin IVA-resistant EPP component was detected, which was only partially blocked by calciseptine (1 micro M), a specific L-type VDCC blocker. 4 Altogether, these data demonstrate that multiple VDCC subtypes are present at the mouse NMJ and that a resistant component can be identified under 'pharmacological' and/or 'pathological' conditions.
Giovannini
F
F
Neuroscience Group, Institute of Molecular Medicine, John Radcliffe Hospital, Headington OX3 9DU, UK. F.Giovannini@ucl.ac.uk
Sher
E
E
Webster
R
R
Boot
J
J
Lang
B
B
D015761:4-Aminopyridine / Q000494:pharmacology*; D000109:Acetylcholine / Q000378:metabolism*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D001323:Autoantibodies / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000502:physiology; D020864:Calcium Channels, N-Type / Q000187:drug effects / Q000502:physiology; D020865:Calcium Channels, P-Type / Q000187:drug effects / Q000502:physiology; D020907:Calcium Channels, Q-Type / Q000187:drug effects / Q000502:physiology; D020908:Calcium Channels, R-Type / Q000187:drug effects / Q000502:physiology; D005260:Female; D006801:Humans; D007074:Immunoglobulin G / Q000494:pharmacology; D066298:In Vitro Techniques; D015624:Lambert-Eaton Myasthenic Syndrome / Q000276:immunology*; D008297:Male; D051379:Mice; D008875:Middle Aged; D009469:Neuromuscular Junction / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D026902:Potassium Channel Blockers / Q000494:pharmacology*
D001323:Autoantibodies; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D020864:Calcium Channels, N-Type; D020865:Calcium Channels, P-Type; D020907:Calcium Channels, Q-Type; D020908:Calcium Channels, R-Type; D007074:Immunoglobulin G; D026902:Potassium Channel Blockers; D015761:4-Aminopyridine; D000109:Acetylcholine