Yuki Wada

Miyazaki University, Миядзаки, Miyazaki, Japan

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Publications (3)5.81 Total impact

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    ABSTRACT: Tetraethylammonium (TEA)-sensitive potassium currents in the cochlear inner hair cells (IHCs) possess the kinetics of fast inactivation. Some enzymes using for IHCs dissociation affect these inactivation kinetics. IHCs were dissociated from guinea-pig cochlea by 1 mg/ml trypsin or 0.25 mg/ml protease VIII, and the properties of the K+ currents were compared using conventional whole-cell voltage-clamp recordings. TEA-sensitive potassium currents showed fast inactivation kinetics in both trypsin-dissociated cells and protease VIII-dissociated cells. The time constant of the inactivation phase in trypsin-treated cells was similar to that in protease VIII-treated cells. However, the rate of inactivation (compared by the ratio between the steady-state current and initial peak current) in protease VIII-treated cells was larger than that in trypsin-treated cells. In protease VIII-dissociated cells, the time constant of recovery from inactivation elucidated by paired-pulse protocol was 3.5 ms. Papain is another enzyme that is sometimes used for dissociating IHCs, so effects of papain were observed. Extracellular papain application (8 unit/ml) demonstrated a slight increase of the outward potassium currents.
    Hearing Research 02/2005; 199(1-2):135-9. DOI:10.1016/j.heares.2004.08.020 · 2.97 Impact Factor
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    ABSTRACT: Using conventional whole-cell voltage-clamp recordings, we examined the 4-aminopyridine (4-AP)- and tetraethylammonium (TEA)-sensitive K(+) currents in the cochlear inner hair cells (IHCs) of guinea pigs. 4-AP-sensitive currents were activated slowly and sustained the same current level, whereas TEA-sensitive currents were activated rapidly, followed by inactivation. The inactivation time course of TEA-sensitive currents was voltage-dependent, becoming faster at more depolarized levels. The inactivation of TEA-sensitive currents almost recovered within 5 ms. 4-AP- and TEA-sensitive K(+) currents coexisted in the same IHC.
    Acta oto-laryngologica. Supplementum 09/2004; 124(553):28-32. DOI:10.1080/03655230410017625
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    ABSTRACT: We investigated the direct action of glutamate (Glu) on the membrane current of isolated inner hair cells of guinea-pig cochlea. Glu elicited inward currents at a holding potential of -70 mV. Eight of 13 cells showed a steady inward current, while five of 13 cells showed a fast and rapidly desensitized current. I-V relationships demonstrated that the reversal potential of Glu-induced current was near 0 mV. Glu-induced currents were dose-dependent, where the half maximum concentration (K(d)) was 41 microM and Hill coefficient (n) was 1.75.
    Brain Research 07/2003; 976(1):135-8. DOI:10.1016/S0006-8993(03)02756-2 · 2.84 Impact Factor