The Ca2+ channel subunit beta2 regulates Ca2+ channel abundance and function in inner hair cells and is required for hearing.
Hearing relies on Ca(2+) influx-triggered exocytosis in cochlear inner hair cells (IHCs). Here we studied the role of the Ca(2+) channel subunit Ca(V)beta(2) in hearing. Of the Ca(V)beta(1-4) mRNAs, IHCs predominantly contained Ca(V)beta(2). Hearing was severely impaired in mice lacking Ca(V)beta(2) in extracardiac tissues (Ca(V)beta(2)(-/-)). This involved deficits in cochlear amplification and sound encoding. Otoacoustic emissions were reduced or absent in Ca(V)beta(2)(-/-) mice, which showed strongly elevated auditory thresholds in single neuron recordings and auditory brainstem response measurements. Ca(V)beta(2)(-/-) IHCs showed greatly reduced exocytosis (by 68%). This was mostly attributable to a decreased number of membrane-standing Ca(V)1.3 channels. Confocal Ca(2+) imaging revealed presynaptic Ca(2+) microdomains albeit with much lower amplitudes, indicating synaptic clustering of fewer Ca(V)1.3 channels. The coupling of the remaining Ca(2+) influx to IHC exocytosis appeared unaffected. Extracellular recordings of sound-evoked spiking in the cochlear nucleus and auditory nerve revealed reduced spike rates in the Ca(V)beta(2)(-/-) mice. Still, sizable onset and adapted spike rates were found during suprathreshold stimulation in Ca(V)beta(2)(-/-) mice. This indicated that residual synaptic sound encoding occurred, although the number of presynaptic Ca(V)1.3 channels and exocytosis were reduced to one-third. The normal developmental upregulation, clustering, and gating of large-conductance Ca(2+) activated potassium channels in IHCs were impaired in the absence of Ca(V)beta(2). Moreover, we found the developmental efferent innervation to persist in Ca(V)beta(2)-deficient IHCs. In summary, Ca(V)beta(2) has an essential role in regulating the abundance and properties of Ca(V)1.3 channels in IHCs and, thereby, is critical for IHC development and synaptic encoding of sound.
Neef
Jakob
J
InnerEarLab, Department of Otolaryngology and Center for Molecular Physiology of the Brain, Göttingen Graduate School for Neurosciences and Molecular Biosciences, 37099 Göttingen, Germany.
Gehrt
Anna
A
Bulankina
Anna V
AV
Meyer
Alexander C
AC
Riedel
Dietmar
D
Gregg
Ronald G
RG
Strenzke
Nicola
N
Moser
Tobias
T
D000161:Acoustic Stimulation / Q000379:methods; D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D001030:Apamin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000172:deficiency / Q000502:physiology*; D020013:Calcium Signaling / Q000187:drug effects / Q000235:genetics; D002586:Cesium / Q000494:pharmacology; D002614:Chelating Agents / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D004558:Electric Stimulation / Q000379:methods; D016057:Evoked Potentials, Auditory, Brain Stem / Q000235:genetics; D005089:Exocytosis / Q000187:drug effects; D006199:Hair Cells, Auditory, Inner / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017084:Otoacoustic Emissions, Spontaneous / Q000235:genetics; D010320:Parvalbumins / Q000378:metabolism; D018408:Patch-Clamp Techniques / Q000379:methods
C485995:Cacna1d protein, mouse; C491528:Cacnb2 protein, mouse; D020746:Calcium Channels, L-Type; D002614:Chelating Agents; D002712:Chlorides; D051036:Large-Conductance Calcium-Activated Potassium Channels; D010320:Parvalbumins; D002586:Cesium; D001030:Apamin; D004533:Egtazic Acid; C028019:cesium chloride; D002118:Calcium