title: Differential localization of voltage-dependent calcium channel alpha1 subunits at the human and rat neuromuscular junction.
abstract: Neurotransmitter release is regulated by voltage-dependent calcium channels (VDCCs) at synapses throughout the nervous system. At the neuromuscular junction (NMJ) electrophysiological and pharmacological studies have identified a major role for P- and/or Q-type VDCCs in controlling acetylcholine release from the nerve terminal. Additional studies have suggested that N-type channels may be involved in neuromuscular transmission. VDCCs consist of pore-forming alpha1 and regulatory beta subunits. In this report, using fluorescence immunocytochemistry, we provide evidence that immunoreactivity to alpha1A, alpha1B, and alpha1E subunits is present at both rat and human adult NMJs. Using control and denervated rat preparations, we have been able to establish that the subunit thought to correspond to P/Q-type channels, alpha1A, is localized presynaptically in discrete puncta that may represent motor nerve terminals. We also demonstrate for the first time that alpha1A and alpha1B (which corresponds to N-type channels) may be localized in axon-associated Schwann cells and, further, that the alpha1B subunit may be present in perisynaptic Schwann cells. In addition, the alpha1E subunit (which may correspond to R/T-type channels) seems to be localized postsynaptically in the muscle fiber membrane and concentrated at the NMJ. The possibility that all three VDCCs at the NMJ are potential targets for circulating autoantibodies in amyotrophic lateral sclerosis is discussed.
authors.affiliation: MRC Neurochemical Pathology Unit, Newcastle General Hospital, Newcastle upon Tyne NE4 6BE, United Kingdom.
authors.forename: N C
authors.initials: NC
authors.lastname: Day
authors.forename: S J
authors.initials: SJ
authors.lastname: Wood
authors.forename: P G
authors.initials: PG
authors.lastname: Ince
authors.forename: S G
authors.initials: SG
authors.lastname: Volsen
authors.forename: W
authors.initials: W
authors.lastname: Smith
authors.forename: C R
authors.initials: CR
authors.lastname: Slater
authors.forename: P J
authors.initials: PJ
authors.lastname: Shaw
mesh_terms: D000690:Amyotrophic Lateral Sclerosis / Q000473:pathology; D000818:Animals; D000918:Antibody Specificity; D015220:Calcium Channels / Q000737:chemistry / Q000502:physiology*; D005260:Female; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology*; D018613:Microscopy, Confocal; D009046:Motor Neurons / Q000737:chemistry / Q000502:physiology; D009121:Muscle Denervation; D018482:Muscle, Skeletal / Q000737:chemistry / Q000166:cytology / Q000294:innervation; D016900:Neurofilament Proteins / Q000032:analysis / Q000276:immunology; D009469:Neuromuscular Junction / Q000737:chemistry* / Q000166:cytology / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012583:Schwann Cells / Q000502:physiology; D012584:Sciatic Nerve / Q000737:chemistry / Q000502:physiology / Q000648:ultrastructure
chemical_list: D015220:Calcium Channels; D016900:Neurofilament Proteins