Erostegui C, Nenov A P, Norris C H, Bobbin R P
Department of Otolaryngology, Tulane University School of Medicine, New Orleans, LA, USA.
Hear Res. 1994 Dec;81(1-2):119-29. doi: 10.1016/0378-5955(94)90159-7.
Acetylcholine (ACh), the major neurotransmitter released by efferent nerve fibers in the cochlea, has been shown to activate a Ca(2+)-dependent K+ conductance in outer hair cells (OHCs). Previously we reported that this ACh operated conductance is permeable to Cs+. The purpose of the present study was to characterize further this Cs(+)-permeable channel and its dependency on Ca2+ using isolated OHCs and the patch clamp technique in the whole cell configuration. The changes in the ACh response were examined when Cs+, Ba2+, Cd2+, N-methyl-D-glucamine (NMG+) and tetraethylammonium (TEA+) were placed in the external or internal solutions. Cs+ substituted for K+ in carrying the ACh-evoked Ca(2+)-dependent K+ current. When NMG+/TEA+ was substituted for internal K+ ACh-evoked an inward and an outward current, and Cs+ substituted for external K+ blocked the outward but not the inward current evoked by ACh suggesting it was carried by K+. In the NMG+/TEA+ condition, when the cell was held at different Vh values for an extended period of time, the ACh-induced K+ current rectified. In Ba2+ (3 mM) with zero Ca2+ ACh failed to induce any detectable current and the ACh response slowly recovered from the Ba2+ block, suggesting a block at an intracellular site. Cd2+ (1 mM) readily and reversibly blocked ACh-induced currents even when carried by Cs+. This data suggests that ACh opens a channel selective for K+, conductive to Cs+ and dependent on Ca2+.
乙酰胆碱（ACh）是耳蜗传出神经纤维释放的主要神经递质，已被证明可激活外毛细胞（OHC）中一种Ca(2+)依赖性K+电导。此前我们报道，这种由ACh调控的电导对Cs+具有通透性。本研究的目的是使用分离的OHC和全细胞模式的膜片钳技术，进一步表征这种Cs(+)通透通道及其对Ca2+的依赖性。当将Cs+、Ba2+、Cd2+、N-甲基-D-葡萄糖胺（NMG+）和四乙铵（TEA+）置于细胞外或细胞内溶液中时，检测ACh反应的变化。Cs+替代K+来携带ACh诱发的Ca(2+)依赖性K+电流。当用NMG+/TEA+替代细胞内K+时，ACh诱发内向和外向电流，而用Cs+替代细胞外K+则阻断ACh诱发的外向电流，但不阻断内向电流，提示内向电流由K+携带。在NMG+/TEA+条件下，当细胞在不同的钳制电压（Vh）值下保持较长时间时，ACh诱发的K+电流发生整流。在含3 mM Ba2+且Ca2+浓度为零的溶液中，ACh未能诱发任何可检测到的电流，且ACh反应从Ba2+阻断中缓慢恢复，提示在细胞内位点发生阻断。即使由Cs+携带，1 mM Cd2+也能迅速且可逆地阻断ACh诱发的电流。这些数据表明，ACh打开了一个对K+选择性通透、对Cs+导电且依赖于Ca2+的通道。
