豚鼠Ⅱ型前庭毛细胞ACh-敏感性BK电流

目的研究豚鼠球囊和椭圆囊Ⅱ型前庭毛细胞乙酰胆碱(ACh)-敏感性钾电流的特性。方法应用全细胞膜片钳技术检测新鲜单离的豚鼠球囊和椭圆囊Ⅱ型前庭毛细胞ACh-敏感性钾电流的离子特性及其药理学特点。结果①细胞外ACh激活一缓慢持久的外向性电流,其效应呈浓度依赖性,半数激活浓度为45μmol.L-1。②ACh-敏感性钾电流对钾通道阻断剂TEA(tetraethylammon ium)、IBTX(ibe-riotoxin)和Cs+敏感,而对4-AP(4-am inopyride)和apam in不敏感。③细胞内应用钙离子螯合剂BAPTA[b is(2-am inophe-noxy)ethane-N,N,N,′N-t′etra-acetic ac id],ACh-敏感性钾电流的幅值迅速被抑制。④ACh-敏感性钾电流对细胞外液中钙离子浓度变化敏感,0.2 mmol.L-1低钙外液中ACh-敏感性钾电流被抑制,电流最大值由0~10 mV向-20 mV~-30 mV超极化方向移动。结论细胞外ACh激活豚鼠球囊和椭圆囊Ⅱ型前庭毛细胞产生大电导钙依赖性钾电流(BK)。ACh-敏感性BK电流在豚鼠Ⅱ型前庭毛细胞超极化保护机制中具有重要的作用。

ACh-sensitive BK current in guinea pig type Ⅱ vestibular hair cells

Aim The nature of the α9-containing nicotinic ACh receptor(α9-nAChR)-mediated small-conductance,calcium-dependent potassium current(SK)in outer hair cells of guinea pigs and saccular hair cells of bullfrog was well-documented.Recently,we reported the slow and sustained calcium-dependent potassium current stimulated by ACh was located in type Ⅱ vestibular hair cells of guinea pigs.Therefore,the nature of the ACh-sensitive potassium current in type II vestibular hair cells of guinea pig saccular macula and utricle macula was explored.Methods Under the whole-cell patch clamp mode,the pharmacology properties and the ions feature of the ACh-sensitive potassium current were investigated.Result Following extracellular perfusion of ACh,type Ⅱ vestibular hair cells displayed a slow and sustained outward current.The ACh-sensitive potassium current showed a dose-dependent way with a half-activation concentration(EC_(50)) of 45 μmol·L~(-1).The ACh-sensitive potassium current was inhibited by extracellular TEA(tetraethylammonium,5 mmol·L~(-1)),potently inhibited by extracellular IBTX(iberiotoxin,200 nmol·L~(-1)),and completely abolished by intracellular Cs~+.However,the ACh-sensitive potassium current was not sensitive to extracellular 4-AP(4-aminopyride,15 μmol·L~(-1)) and apamin(1 μmol·L~(-1)).The current amplitude of the ACh-sensitive potassium current was potently inhibited by intracellular application of BAPTA[bis(2-aminophenoxy] ethane-N,N,N′,N′-tetra-acetic acid).Furthermore,the ACh-sensitive potassium current was strongly inhibited by lowering of extracellular calcium concentration from 2 mmol·L~(-1) to 0.2 mmol·L~(-1) with a maximum shifted toward hyperpolarized potential from 0～10 mV to-20 mV～-30 mV.Conclusion Extracellular application of ACh activated the BK current.The ACh-sensitive BK current might play an important role in the synaptic inhibition of type Ⅱ vestibular hair cells of guinea pigs saccular macula and utricle macula.