RESUMO
<p><b>OBJECTIVE</b>To investigate the pharmacological modulatory properties of noradrenaline in the rat spiral ganglion neuron.</p><p><b>METHODS</b>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.</p><p><b>RESULTS</b>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.</p><p><b>CONCLUSIONS</b>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.</p>