Gentamicin blocks the ACh-induced BK current in guinea pig type II vestibular hair cells by competing with Ca²⁺ at the L-type calcium channel.
Type II vestibular hair cells (VHCs II) contain big-conductance Ca²⁺-dependent K⁺ channels (BK) and L-type calcium channels. Our previous studies in guinea pig VHCs II indicated that acetylcholine (ACh) evoked the BK current by triggering the influx of Ca²⁺ ions through L-type Ca²⁺ channels, which was mediated by M2 muscarinic ACh receptor (mAChRs). Aminoglycoside antibiotics, such as gentamicin (GM), are known to have vestibulotoxicity, including damaging effects on the efferent nerve endings on VHCs II. This study used the whole-cell patch clamp technique to determine whether GM affects the vestibular efferent system at postsynaptic M2-mAChRs or the membrane ion channels. We found that GM could block the ACh-induced BK current and that inhibition was reversible, voltage-independent, and dose-dependent with an IC₅₀ value of 36.3 ± 7.8 µM. Increasing the ACh concentration had little influence on GM blocking effect, but increasing the extracellular Ca²⁺ concentration ([Ca²⁺]₀) could antagonize it. Moreover, 50 µM GM potently blocked Ca²⁺ currents activated by (-)-Bay-K8644, but did not block BK currents induced by NS1619. These observations indicate that GM most likely blocks the M2 mAChR-mediated response by competing with Ca²⁺ at the L-type calcium channel. These results provide insights into the vestibulotoxicity of aminoglycoside antibiotics on mammalian VHCs II.
Department of Otorhinolaryngology, Union Hospital of Tongji Medical College, Hua-Zhong University of Science and Technology, 1277 Jiefang Avenue, Wuhan 430022, China. yuhong_0706@163.com.
Hong
H
Yu
Department of Otorhinolaryngology, Union Hospital of Tongji Medical College, Hua-Zhong University of Science and Technology, 1277 Jiefang Avenue, Wuhan 430022, China. ckguo2255@sina.com.
Chang-Kai
CK
Guo
Department of Otorhinolaryngology, Union Hospital of Tongji Medical College, Hua-Zhong University of Science and Technology, 1277 Jiefang Avenue, Wuhan 430022, China. entwy821@163.com.
Yi
Y
Wang
Department of Otorhinolaryngology, Union Hospital of Tongji Medical College, Hua-Zhong University of Science and Technology, 1277 Jiefang Avenue, Wuhan 430022, China. entzt2013@sina.com.
Tao
T
Zhou
Department of Otorhinolaryngology, Union Hospital of Tongji Medical College, Hua-Zhong University of Science and Technology, 1277 Jiefang Avenue, Wuhan 430022, China. entwjkong@hust.edu.cn.
Wei-Jia
WJ
Kong
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D002478:Cells, Cultured; D005839:Gentamicins / Q000494:pharmacology*; D006168:Guinea Pigs; D018069:Hair Cells, Vestibular / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000378:metabolism*; D043585:Receptor, Muscarinic M2 / Q000378:metabolism
D020746:Calcium Channels, L-Type; D005839:Gentamicins; D015221:Potassium Channels; D043585:Receptor, Muscarinic M2; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D000109:Acetylcholine; D002118:Calcium