title: Spectrum of Cav1.4 dysfunction in congenital stationary night blindness type 2.
abstract: Defective retinal synaptic transmission in patients affected with congenital stationary night blindness type 2 (CSNB2) can result from different dysfunction phenotypes in Cav1.4 L-type calcium channels. Here we investigated two prototypical Cav1.4 variants from either end of the functional spectrum. Using whole-cell and single-channel patch-clamp techniques, we provide analysis of the biophysical characteristics of the point mutation L860P and the C-terminal truncating mutation R1827X. L860P showed a typical loss-of-function phenotype attributed to a reduced number of functional channels expressed at the plasma membrane as implied by gating current and non-stationary noise analyses. This phenotype can be rationalized, because the inserted proline is predicted to break an amphipatic helix close to the transmembrane segment IIIS1 and thus to reduce channel stability and promote misfolding. In fact, L860P was subject to an increased turnover. In contrast, R1827X displayed an apparent gain-of-function phenotype, i.e., due to a hyperpolarizing shift of the IV-curve and increased single-channel activity. However, truncation also resulted in the loss of functional C-terminal modulation and thus unmasked calcium-dependent inactivation. Thus R1827X failed to support continuous calcium influx. Current inactivation curtails the dynamic range of photoreceptors (e.g., when adapting to variation in illumination). Taken together, the analysis of two representative mutations that occur in CSNB2 patients revealed fundamental differences in the underlying defect. These may explain subtle variations in the clinical manifestation and must be taken into account, if channel function is to be restored by pharmacochaperones or related approaches.
authors.affiliation: Medical University Vienna, Center for Physiology and Pharmacology, Department of Neurophysiology and -pharmacology, Schwarzspanierstrasse 17, 1090 Vienna, Austria.
authors.forename: Verena
authors.initials: V
authors.lastname: Burtscher
authors.affiliation: Medical University Vienna, Center for Physiology and Pharmacology, Department of Neurophysiology and -pharmacology, Schwarzspanierstrasse 17, 1090 Vienna, Austria.
authors.forename: Klaus
authors.initials: K
authors.lastname: Schicker
authors.affiliation: University of Cologne, Department of Pharmacology and Center of Molecular Medicine, 50931 Cologne, Germany.
authors.forename: Elena
authors.initials: E
authors.lastname: Novikova
authors.affiliation: Medical University Vienna, Center for Physiology and Pharmacology, Department of Neurophysiology and -pharmacology, Schwarzspanierstrasse 17, 1090 Vienna, Austria.
authors.forename: Birgit
authors.initials: B
authors.lastname: Pöhn
authors.affiliation: Medical University Vienna, Center for Physiology and Pharmacology, Department of Pharmacology, Währingerstrasse 13A, 1090 Wien, Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Stockner
authors.affiliation: Medical University Vienna, Center for Physiology and Pharmacology, Department of Neurophysiology and -pharmacology, Schwarzspanierstrasse 17, 1090 Vienna, Austria.
authors.forename: Christof
authors.initials: C
authors.lastname: Kugler
authors.affiliation: University of Innsbruck, Institute of Pharmacy, Pharmacology and Toxicology, Center for Chemistry and Biomedicine, Innrain 80-82/III, 6020 Innsbruck, Austria.
authors.forename: Anamika
authors.initials: A
authors.lastname: Singh
authors.affiliation: INSERM, UMR_S968, Paris F-75012, France; CNRS, UMR_7210, Paris F-75012, France; UPMC Univ Paris 06, UMR_S 968, Institut de la Vision, Paris F-75012, France.
authors.forename: Christina
authors.initials: C
authors.lastname: Zeitz
authors.affiliation: INSERM, UMR_S968, Paris F-75012, France; CNRS, UMR_7210, Paris F-75012, France; UPMC Univ Paris 06, UMR_S 968, Institut de la Vision, Paris F-75012, France.
authors.forename: Marie-Elise
authors.initials: ME
authors.lastname: Lancelot
authors.affiliation: INSERM, UMR_S968, Paris F-75012, France; CNRS, UMR_7210, Paris F-75012, France; UPMC Univ Paris 06, UMR_S 968, Institut de la Vision, Paris F-75012, France; Centre Hospitalier National d'Ophtalmologie des Quinze-Vingts, INSERM-DHOS CIC 503, Paris F-75012, France; UCL-Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Audo
authors.affiliation: Dept of Ophthalmology & Center for Medical Genetics, Ghent University Hospital & Ghent University, 9000 Ghent, Belgium.
authors.forename: Bart Peter
authors.initials: BP
authors.lastname: Leroy
authors.affiliation: Medical University Vienna, Center for Physiology and Pharmacology, Department of Pharmacology, Währingerstrasse 13A, 1090 Wien, Austria.
authors.forename: Michael
authors.initials: M
authors.lastname: Freissmuth
authors.affiliation: University of Cologne, Department of Pharmacology and Center of Molecular Medicine, 50931 Cologne, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Herzig
authors.affiliation: University of Cologne, Department of Pharmacology and Center of Molecular Medicine, 50931 Cologne, Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Matthes
authors.affiliation: Medical University Vienna, Center for Physiology and Pharmacology, Department of Neurophysiology and -pharmacology, Schwarzspanierstrasse 17, 1090 Vienna, Austria. Electronic address: alexandra.koschak@meduniwien.ac.at.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Koschak
mesh_terms: D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000235:genetics* / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002648:Child; D003001:Cloning, Molecular; D015785:Eye Diseases, Hereditary / Q000235:genetics* / Q000378:metabolism; D040181:Genetic Diseases, X-Linked / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D008297:Male; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics*; D009216:Myopia / Q000235:genetics* / Q000378:metabolism; D009755:Night Blindness / Q000235:genetics* / Q000378:metabolism; D018408:Patch-Clamp Techniques; D017386:Sequence Homology, Amino Acid
chemical_list: C113330:CACNA1F protein, human; D020746:Calcium Channels, L-Type; D002118:Calcium
keywords: Calcium channelopathy; Cav1.4; Congenital stationary night blindness type 2; L-type calcium channel