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Pathogenic point mutations in a transmembrane domain of the ε subunit increase the Ca 2+ permeability of the human endplate ACh receptor
Author(s) -
Castro Amalia Di,
Martinello Katiuscia,
Grassi Francesca,
Eusebi Fabrizio,
Engel Andrew G.
Publication year - 2007
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2007.127977
Subject(s) - receptor , acetylcholine receptor , protein subunit , mutant , transmembrane domain , biophysics , chemistry , point mutation , transmembrane protein , stimulation , ion channel , microbiology and biotechnology , biology , endocrinology , biochemistry , gene
The ε subunit of the human endplate ACh receptor (AChR) is a key determinant of the large fraction of the ACh‐evoked current carried by Ca 2+ ions ( P f ). Consequently, missense mutations in the ε subunit are potential targets for altering the P f of human AChR. In this paper we investigate the effects of two pathogenic point mutations in the M2 transmembrane segment AChR ε subunit, εT264P and εV259F, that cause slow‐channel syndromes (SCS). When expressed in GH4C1 cells, the mutant receptors subunits raise Ca 2+ permeability of the receptors ∼1.5 and ∼2‐fold above that of wild‐type, to attain P f values of 11.8% (εT264P) and 15.4% (εV259F). The latter value exceeds most P f values reported to date for ligand‐gated ion channels. Consistent with these findings, the biionic Ca 2+ permeability ratio ( P Ca / P Cs ) of the mutant AChRs is also increased. Upon repetitive stimulation with ACh, the mutant receptors show an enhanced current run‐down compared with wild‐type, leading to a strong reduction of their function. We propose that the enhanced Ca 2+ permeability of the mutant receptors overrides the protective effect of desensitization and, together with the prolonged opening events of the AChR channel, is an important determinant of the excitotoxic endplate damage in the SCS.