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Guo CK, Kong WJ, Yu QS, Li GQ, Li JL, Li QT: [Feature of ACh-sensitive potassium current in outer hair cells of guinea pig cochlea]. Zhonghua Er Bi Yan Hou Tou Jing Wai Ke Za Zhi. 2007 Apr;42(4):286-90.
OBJECTIVE: To explore the feature of the ACh-sensitive potassium current in guinea pig cochlear outer hair cells. METHODS: Cochlear outer hair cells of guinea pigs (n=38) were isolated by collagenase type IV. Under the whole-cell patch mode, the ions nature and the pharmacological properties of the ACh-sensitive potassium current were investigated by applying the inhibitors of calcium-dependent potassium currents and the inhibitors of nicotinic ACh receptor. RESULTS: Following application of ACh, cochlear outer hair cells displayed a rapidly activating outward potassium current with a fast desensitized kinetic and a reversal (x +/- s) potential of (-67.3 +/- 8.2) mV (n=10). At the holding potential of -50 mV, the current amplitude of ACh-sensitive potassium current activated by 100 micronmol/L ACh was (506.6 +/- 186.3) pA (n=9). ACh-sensitive potassium current was sensitive to TEA (tetraethylammonium chloride, 10 mmol/L) and potently inhibited by the small conductance calcium-dependent potassium current (SK) blocker, apamin (1 micromol/L). Iberiotoxin (IBTX), the well-known blocker of big conductance calcium-dependent potassium current (BK), failed to inhibit the amplitude of the ACh-sensitive potassium current at the dose of 200 nmol/L. The dose for half-maximal response (EC50) of the ACh-sensitive potassium current was (33.5 +/- 5.7) micromol/L (n=7). The ACh-sensitive potassium current was sensitive to the GABA (gamma-aminobutyric acid)-A receptor blocker, bicuculline, and strongly inhibited by the selective blocker of the alpha 9-nicotinic ACh receptor, strychnine. Strychnine and bicuculline showed the dose-dependent blocking effect with a half inhibition-maximal response (IC50) of (22.3 +/- 2.6) nmol/L (n=7) and (1.2 +/- 0.4) micromol/L (n=6), respectively. CONCLUSIONS: This work provides direct evidences that the ACh-sensitive SK current was present on guinea pig cochlear outer hair cells. The activation of the ACh-sensitive SK current was most possibly mediated by a alpha 9-nicotinic ACh receptor. |
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