Calcium channels in mouse hair cells: function, properties and pharmacology.
Adult inner hair cells (IHCs) possess voltage-activated Ca2+ currents that couple receptor potentials to transmitter release at the afferent synapses. Before the onset of hearing both IHCs and outer hair cells (OHCs) exhibit Ca2+ currents. More than 90% of neonatal hair cell (HC) currents flow through alpha1D Ca2+ channel subunits because they are absent in both IHCs and OHCs from alpha1D-/- mice and residual currents are insensitive to L-type agonists. Since lack of the alpha1D-subunit leads to HC degeneration and profound deafness, class D L-type Ca2+ currents seem to be crucial for the development and functioning of the inner ear. Neonatal HC Ca2+ currents were studied using the whole-cell patch clamp technique. They showed rapid activation, rapid deactivation and very little inactivation. They started activating as negative as -65mV. In contrast to alpha1C-mediated (classical L-type) Ca2+ currents, they showed a rather low sensitivity to various L-type antagonists. 10 microM nifedipine e.g. blocked HC Ca2+ currents by about 40% whereas class C L-type Ca2+ currents are completely blocked by 100nM nifedipine. The L-type channel agonist Bay K 8644 increased the HC Ca2+ current by 100-200% and shifted the IV curve to more negative potentials which is similar to its effects in alpha1C-mediated Ca2+ currents.
Engel
Jutta
J
Institute of Physiology II and Department of Sensory Biophysics of the ENT Clinic, University of Tübingen, Germany. jutta.engel@uni-tuebingen.de
Michna
Marcus
M
Platzer
Josef
J
Striessnig
Jörg
J
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism / Q000502:physiology*; D006198:Hair Cells, Auditory / Q000187:drug effects / Q000378:metabolism*; D018072:Hair Cells, Auditory, Outer / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D009543:Nifedipine / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D009543:Nifedipine