[Inhibition of gamma-aminobutyric acid receptor-gated chloride currents by noradrenaline in rat spiral ganglion neuron].
OBJECTIVE
To investigate the pharmacological modulatory properties of noradrenaline in the rat spiral ganglion neuron.


METHODS
Nystatin perforated patch recording technique under voltage-clamp conditions was used to record the modulatory effect of noradrenaline on the current evoked by gamma-amino butyric acid (GABA) in the spiral ganglion neuron.


RESULTS
The reversal potential of the GABA response was about (- 0.78 +/- 0.05) mV (n = 8), which was almost identical to the theoretical Cl- equilibrium potential. At the holding potential of -50 mV, GABA evoked inward current (I(GABA)) over the concentration range of 0.3 to 1 micromol/L. The EC50 and Hill coefficient for GABA were (5.2 +/- 0.5) micromol/L and 1.03 (n = 26). The I(GABA) was suppressed by bicuculline, the selective GABA-A receptor antagonist, and the chloride currents evoked by GABA was inhibited by noradrenaline.


CONCLUSIONS
The result indicates that noradrenaline depressed GABA-A receptor-gated chloride currents, which may contribute to the modulatory effect of sympathetic system on auditory transmission.
Zha
Ding-Jun
DJ
Department of Otorhinolaryngology Head and Neck Surgery, Xijing Hospital, Fourth Military Medical University of Chinese People's Liberation Army, Xi'an 710032, China.
Xue
Tao
T
Qiao
Li
L
Lu
Lian-Jun
LJ
Lin
Ying
Y
Wang
Zhi-Ming
ZM
Li
Yun-Qing
YQ
Qiu
Jian-Hua
JH
D000818:Animals; D018118:Chloride Channels / Q000187:drug effects*; D058787:GABA-A Receptor Antagonists / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D009638:Norepinephrine / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D018079:Receptors, GABA / Q000378:metabolism; D013136:Spiral Ganglion / Q000187:drug effects*
D018118:Chloride Channels; D058787:GABA-A Receptor Antagonists; D018079:Receptors, GABA; D009638:Norepinephrine