title: EF-hand protein Ca2+ buffers regulate Ca2+ influx and exocytosis in sensory hair cells.
abstract: EF-hand Ca(2+)-binding proteins are thought to shape the spatiotemporal properties of cellular Ca(2+) signaling and are prominently expressed in sensory hair cells in the ear. Here, we combined genetic disruption of parvalbumin-α, calbindin-D28k, and calretinin in mice with patch-clamp recording, in vivo physiology, and mathematical modeling to study their role in Ca(2+) signaling, exocytosis, and sound encoding at the synapses of inner hair cells (IHCs). IHCs lacking all three proteins showed excessive exocytosis during prolonged depolarizations, despite enhanced Ca(2+)-dependent inactivation of their Ca(2+) current. Exocytosis of readily releasable vesicles remained unchanged, in accordance with the estimated tight spatial coupling of Ca(2+) channels and release sites (effective "coupling distance" of 17 nm). Substitution experiments with synthetic Ca(2+) chelators indicated the presence of endogenous Ca(2+) buffers equivalent to 1 mM synthetic Ca(2+)-binding sites, approximately half of them with kinetics as fast as 1,2-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA). Synaptic sound encoding was largely unaltered, suggesting that excess exocytosis occurs extrasynaptically. We conclude that EF-hand Ca(2+) buffers regulate presynaptic IHC function for metabolically efficient sound coding.
authors.affiliation: Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, 37099 Göttingen, Germany; Collaborative Research Center 889, University of Göttingen, 37099 Göttingen, Germany; tpangrs@gwdg.de nstrenzke@med.uni-goettingen.de tmoser@gwdg.de.
authors.forename: Tina
authors.initials: T
authors.lastname: Pangršič
authors.affiliation: Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, 37099 Göttingen, Germany; Theoretical Neurophysics Group, Max Planck Institute for Dynamics and Self-Organization, 37077 Göttingen, Germany; Bernstein Center for Computational Neuroscience, Göttingen University, 37077 Göttingen, Germany;
authors.forename: Mantas
authors.initials: M
authors.lastname: Gabrielaitis
authors.affiliation: Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, 37099 Göttingen, Germany; Collaborative Research Center 889, University of Göttingen, 37099 Göttingen, Germany;
authors.forename: Susann
authors.initials: S
authors.lastname: Michanski
authors.affiliation: Unit of Anatomy, Department of Medicine, University of Fribourg, 1700 Fribourg, Switzerland;
authors.forename: Beat
authors.initials: B
authors.lastname: Schwaller
authors.affiliation: Collaborative Research Center 889, University of Göttingen, 37099 Göttingen, Germany; Theoretical Neurophysics Group, Max Planck Institute for Dynamics and Self-Organization, 37077 Göttingen, Germany; Bernstein Center for Computational Neuroscience, Göttingen University, 37077 Göttingen, Germany;
authors.forename: Fred
authors.initials: F
authors.lastname: Wolf
authors.affiliation: Collaborative Research Center 889, University of Göttingen, 37099 Göttingen, Germany; Auditory Systems Physiology Group, InnerEarLab, Department of Otolaryngology, University Medical Center Göttingen, 37099 Göttingen, Germany; and Eaton Peabody Laboratory, Massachusetts Eye and Ear Infirmary, Harvard University, Boston, MA 02114 tpangrs@gwdg.de nstrenzke@med.uni-goettingen.de tmoser@gwdg.de.
authors.forename: Nicola
authors.initials: N
authors.lastname: Strenzke
authors.affiliation: Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, 37099 Göttingen, Germany; Collaborative Research Center 889, University of Göttingen, 37099 Göttingen, Germany; Bernstein Center for Computational Neuroscience, Göttingen University, 37077 Göttingen, Germany; tpangrs@gwdg.de nstrenzke@med.uni-goettingen.de tmoser@gwdg.de.
authors.forename: Tobias
authors.initials: T
authors.lastname: Moser
mesh_terms: D000818:Animals; D064092:Calbindin 1 / Q000235:genetics / Q000378:metabolism*; D064032:Calbindin 2 / Q000235:genetics / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D006199:Hair Cells, Auditory, Inner / Q000166:cytology / Q000378:metabolism*; D006309:Hearing / Q000187:drug effects / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D010320:Parvalbumins / Q000235:genetics / Q000378:metabolism*; D013569:Synapses / Q000235:genetics / Q000378:metabolism
chemical_list: C576511:Calb2 protein, mouse; D064092:Calbindin 1; D064032:Calbindin 2; D002614:Chelating Agents; D010320:Parvalbumins; D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid
keywords: calcium buffers; calcium current; exocytosis; hair cell; synapse