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This Article Full Text Full Text (PDF) All Versions of this Article: 553/3/747    most recent jphysiol.2003.053256v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Michna, M. Articles by Engel, J. Search for Related Content PubMed PubMed Citation Articles by Michna, M. Articles by Engel, J.

Ca_v1.3 (1D) Ca²⁺ currents in neonatal outer hair cells of mice

Marcus Michna, Martina Knirsch, Jean-Charles Hoda*, Stefan Muenkner, Patricia Langer, Josef Platzer*, Jörg Striessnig* and Jutta Engel

Outer hair cells (OHC) serve as electromechanical amplifiers that guarantee the unique sensitivity and frequency selectivity of the mammalian cochlea. It is unknown whether the afferent fibres connected to adult OHCs are functional. If so, voltage-activated Ca²⁺ channels would be required for afferent synaptic transmission. In neonatal OHCs, Ca²⁺ channels seem to play a role in maturation since OHCs from Ca_v1.3-deficient (Ca_v1.3^-/-) mice degenerate shortly after the onset of hearing. We therefore studied whole-cell Ca²⁺ currents in outer hair cells aged between postnatal day 1 (P1) and P8. OHCs showed a rapidly activating inward current that was 1.8 times larger with 10 mM Ba²⁺ as charge carrier (I_Ba) than with equimolar Ca²⁺ (I_Ca). I_Ba started activating at -50 mV with V_max = -1.9 ± 6.9 mV, V_0.5 = -15.0 ± 7.1 mV and k = 8.2 ± 1.1 mV (n = 34). The peak I_Ba showed negligible inactivation (3.6 % after 300 ms) whereas the I_Ca (10 mM Ca²⁺) was inactivated by 50.7 %. OHC I_Ba was reduced by 33.5 ± 10.3 % (n = 14) with 10 µM nifedipine and increased to 178.5 ± 57.8 % (n = 14) by 5 µM Bay K 8644. A dose-response curve for nifedipine revealed an IC₅₀ of 2.3 µM, a Hill coefficient of 2.7 and a maximum block of 36 %. Average I_Ba density in OHCs was 24.4 ± 10.8 pA pF^-1 (n = 105) which is only 38 % of the value in inner hair cells. Single cell RT-PCR revealed expression of Ca_v1.3 in OHCs. In OHCs from Ca_v1.3^-/- mice, Ba²⁺ current density was reduced to 0.6 ± 0.5 pA pF^-1 (n = 9) indicating that > 97 % of the Ca²⁺ channel current in OHCs flows through Ca_v1.3.

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