Reserch of relation between mechanisms of intracellular signaling pathways in cochlear outer and inner hair cells and ototoxic drugs

耳蜗外毛细胞的缓慢缩短被认为是改变耳蜗敏感度的原因。强电场刺激豚鼠分离的外毛细胞可使细胞缩短2-3分钟。电刺激使细胞长度和体积减小，细胞内氯离子浓度降低。细胞松弛素B可抑制电刺激引起的收缩，但不能抑制体积减小。以下化学物质或操作可抑制这些反应：速尿、DIDS、AC9、四乙基铵、轮藻毒素(ChTX)、W-芋螺毒素和无钙培养基。这些结果表明，电刺激引起的外毛细胞缩短和收缩不仅源于肌动蛋白介导的收缩，也源于氯离子通过速尿、DIDS和AC9敏感的Cl-通道外流，以及K+通过ChTX敏感的K+通道外流。而强直电场刺激引起豚鼠耳蜗内毛细胞的显著收缩。这种收缩在刺激后30-40秒出现，持续约1分钟。使用数字成像显微镜和对氯离子敏感的荧光染料N-(6-甲氧基喹啉)乙酸乙酯，细胞体积和细胞内氯离子浓度的减少伴随着细胞收缩。细胞松弛素B抑制了这一事件，表明收缩是由肌动蛋白介导的。

Slow shortening of cochlear outer hair cells has been speculated to modify cochlear sensitivity. Tetanic electrical field stimulation of isolated outer hair cells from guinea pigs shortened the cells for 2-3 min. Electrical stimulation reduced cell length and volume and decreased the intracellular Cl- concentration. Cytochalasin B inhibited electrical stimulation-induced shortening but not volume reduction. The following chemicals or manipulations inhibited the responses : furosemide, DIDS,AC9, tetraethylammonium, charybdotoxin (ChTX), w-conotoxin, and Ca^<2+>_free medium. These findings suggest that both electrical stimulation-induced shortening and shrinkage of outer hair cells result not only from an actin-mediated contractile force, but also from Cl- efflux through furosemide-, DIDS-, and AC9-sensitive Cl- channels, and K+ efflux through ChTX-sensitive K+ channels.While, tetanic electrical field stimulation elicited a prominent contraction of isolated guinea pig cochlear inner hair cells. This contraction appeared 30-40 sec after field stimulation and lasted for about 1 min. Using a digital imaging microscope and the Cl^--sensitive fluorescence dye, N- (6-methoxyquinolyl) acethoethyl ester, the decrease in cell volume and intracellular Cl- concentration were concomitant with the cell contraction. Cytochalasin B inhibited this event, suggesting that the contraction is mediated by actin.