Harada N, Ernst A, Zenner H P
Hearing Research Laboratories, Department of Otolaryngology, University of Tübingen, Germany.
Brain Res. 1993 Jun 18;614(1-2):205-11. doi: 10.1016/0006-8993(93)91036-r.
The electrophysiological responses of isolated guinea pig outer hair cells (OHCs) to hyposmotic activation were studied using the whole-cell patch-clamp technique. The cell swelling by hyposmotic activation hyperpolarized OHCs by 6.6 +/- 2.3 mV from the resting membrane potential of -58.5 +/- 5.9 mV (n = 48). This hyperpolarization was associated with an outward current (97.7 +/- 22.2 pA, n = 15). The hyperpolarization was inhibited by 300 microM quinine, 5 mN Ba2+ and increasing the extracellular K+ to 30 mM from 5 mM. In the absence of extracellular Ca2+ (1 mM EGTA), the hyperpolarization during hyposmotic activation was also abolished while the following depolarization was preserved. 50 microM GdCl3, which is known to block stretch-activated non-specific cation channels, inhibited the hyperpolarization reversibly. 50 microM GdCl3 also inhibited [Ca2+]i increase during hyposmotic activation as shown by the calcium-sensitive dye fura-2. Simultaneously, the [Ca2+]i increase and the hyperpolarization during hyposmotic activation could be observed using the combined method of whole-cell patch clamp and fura-2 technique. It is concluded that the cell swelling by hyposmotic activation may activate the stretch-activated non-specific cation channels in the OHCs which allow a Ca2+ influx. In turn, this [Ca2+]i increase leads to an activation of the Ca(2+)-activated K+ channels at the basolateral membrane of OHCs which results finally in a reversible hyperpolarization of OHCs by K+ efflux.
采用全细胞膜片钳技术研究了豚鼠离体外毛细胞（OHCs）对低渗激活的电生理反应。低渗激活引起的细胞肿胀使OHCs从静息膜电位-58.5±5.9 mV超极化6.6±2.3 mV（n = 48）。这种超极化与外向电流（97.7±22.2 pA，n = 15）相关。300 μM奎宁、5 mM Ba2+以及将细胞外K+浓度从5 mM增加到30 mM可抑制这种超极化。在无细胞外Ca2+（1 mM EGTA）时，低渗激活期间的超极化也消失，而随后的去极化得以保留。已知可阻断牵张激活的非特异性阳离子通道的50 μM GdCl3可可逆性抑制超极化。50 μM GdCl3还可抑制低渗激活期间[Ca2+]i的增加，这由钙敏染料fura-2显示。同时，采用全细胞膜片钳和fura-2技术联合方法可观察到低渗激活期间[Ca2+]i的增加和超极化。结论是，低渗激活引起的细胞肿胀可能激活OHCs中的牵张激活的非特异性阳离子通道，使Ca2+内流。反过来，这种[Ca2+]i的增加导致OHCs基底外侧膜上Ca(2+)-激活的K+通道激活，最终导致K+外流使OHCs发生可逆性超极化。
