RBP2 stabilizes slow Cav1.3 Ca2+ channel inactivation properties of cochlear inner hair cells

Nadine J Ortner, Alexandra Pinggera, Nadja T Hofer, Anita Siller, Niels Brandt, Andrea Raffeiner, Kristina Vilusic, Isabelle Lang, Kerstin Blum, Gerald J Obermair, Eduard Stefan, Jutta Engel, Jörg Striessnig

Research output: Journal article (peer-reviewed)Journal article

8 Citations (Scopus)

Abstract

Cav1.3 L-type Ca2+ channels (LTCCs) in cochlear inner hair cells (IHCs) are essential for hearing as they convert sound-induced graded receptor potentials into tonic postsynaptic glutamate release. To enable fast and indefatigable presynaptic Ca2+ signaling, IHC Cav1.3 channels exhibit a negative activation voltage range and uniquely slow inactivation kinetics. Interaction with CaM-like Ca2+-binding proteins inhibits Ca2+-dependent inactivation, while the mechanisms underlying slow voltage-dependent inactivation (VDI) are not completely understood. Here we studied if the complex formation of Cav1.3 LTCCs with the presynaptic active zone proteins RIM2α and RIM-binding protein 2 (RBP2) can stabilize slow VDI. We detected both RIM2α and RBP isoforms in adult mouse IHCs, where they co-localized with Cav1.3 and synaptic ribbons. Using whole-cell patch-clamp recordings (tsA-201 cells), we assessed their effect on the VDI of the C-terminal full-length Cav1.3 (Cav1.3L) and a short splice variant (Cav1.342A) that lacks the C-terminal RBP2 interaction site. When co-expressed with the auxiliary β3 subunit, RIM2α alone (Cav1.342A) or RIM2α/RBP2 (Cav1.3L) reduced Cav1.3 VDI to a similar extent as observed in IHCs. Membrane-anchored β2 variants (β2a, β2e) that inhibit inactivation on their own allowed no further modulation of inactivation kinetics by RIM2α/RBP2. Moreover, association with RIM2α and/or RBP2 consolidated the negative Cav1.3 voltage operating range by shifting the channel's activation threshold toward more hyperpolarized potentials. Taken together, the association with "slow" β subunits (β2a, β2e) or presynaptic scaffolding proteins such as RIM2α and RBP2 stabilizes physiological gating properties of IHC Cav1.3 LTCCs in a splice variant-dependent manner ensuring proper IHC function.

Original languageEnglish
Pages (from-to)3-25
Number of pages23
JournalPflugers Archiv European Journal of Physiology
Volume472
Issue number1
DOIs
Publication statusPublished - 1 Jan 2020

Keywords

  • Action Potentials
  • Animals
  • Binding Sites
  • Calcium Channels, L-Type/chemistry
  • Female
  • HEK293 Cells
  • Hair Cells, Auditory, Inner/metabolism
  • Humans
  • Intracellular Signaling Peptides and Proteins/metabolism
  • Ion Channel Gating
  • Male
  • Mice
  • Protein Binding

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