Pharmacology of acetylcholine-mediated cell signaling in the lateral line organ following efferent stimulation
Pharmacology of acetylcholine-mediated cell signaling in the lateral line organ following efferent stimulation
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DOI：
10.1152/jn.01283.2004
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发表时间：
2005-05-01
影响因子：
2.5
通讯作者：
Sewell, WF
中科院分区：
文献类型：
--
作者：
Dawkins, R;Keller, SL;Sewell, WF
胆碱能传出纤维改变毛细胞对机械刺激的反应。据推测，钙通过烟碱受体进入毛细胞激活小电导（SK），钙激活钾通道，使毛细胞过度兴奋。钙信号可以通过钙诱导的钙从突触池释放而放大。由于哺乳动物内耳的结构复杂而脆弱，在完整的耳蜗中进行这些想法的药理学测试在技术上是困难的。我们转向非洲爪蟾侧线器官，其简单性和可访问性使其成为在相对完整的系统中理解毛细胞器官功能的模型。将药物施加到皮肤的内表面，同时监测传出刺激对传入纤维放电率的影响。传出效应被SK通道的拮抗剂阻断，包括apamin（EC 50 = 0.5 μ M）和地喹铵（EC 50 = 12 μ M）。共同管理的苯甲基磺酰氟，蛋白水解抑制剂，蜂毒肽的效果没有增强。传出效应被兰尼定减弱，兰尼定是一种可以干扰钙诱导的钙释放的药物，尽管需要相对高浓度（mM）的兰尼定。荧光阳离子苯乙烯基染料，4-di-2-asp和fm 1-43，阻断传出效应，虽然它是不可能观察到的染料进入毛细胞的基础具体。这些药理学研究结果在非洲爪蟾侧线器官支持的假设，传出刺激的影响介导的钙进入通过烟碱受体通过激活SK通道，并建议这种机制的一般性，在冥想胆碱能传出效应。
Cholinergic efferent fibers modify hair cell responses to mechanical stimulation. It is hypothesized that calcium entering the hair cell through a nicotinic receptor activates a small-conductance (SK), calcium-activated potassium channel to hyperpolarize the hair cell. The calcium signal may be amplified by calcium-induced calcium release from the synaptic cisternae. Pharmacological tests of these ideas in the intact cochlea have been technically difficult because of the complex and fragile structure of the mammalian inner ear. We turned to the Xenopus laevis lateral line organ, whose simplicity and accessibility make it a model for understanding hair cell organ function in a relatively intact system. Drugs were applied to the inner surface of the skin while monitoring the effects of efferent stimulation on afferent fiber discharge rate. Efferent effects were blocked by antagonists of SK channels including apamin (EC50 = 0.5 mu M) and dequalinium (EC50 = 12 mu M). The effect of apamin was not enhanced by co-administration of phenylmethylsulfonyl fluoride, a proteolysis inhibitor. Efferent effects were attenuated by ryanodine, an agent that can interfere with calcium-induced calcium release, although relatively high (mM) concentrations of ryanodine were required. Fluorescent cationic styryl dyes, 4-di-2-asp and fm 1-43, blocked efferent effects, although it was not possible to observe specific entry of the dye into the base of hair cells. These pharmacological findings in the Xenopus lateral line organ support the hypothesis that effects of efferent stimulation are mediated by calcium entry through the nicotinic receptor via activation of SK channels and suggest the generality of this mechanism in meditating cholinergic efferent effects.