Local Anesthetics Reduce the Inhibitory Neurotransmitter-induced Current in Dissociated Hippocampal Neurons of the Rat

The effects of local anesthetics on amino acid-induced currents were examined using the whole-cell configuration of the patch clamp technique in dissociated hippocampal pyramidal neurons of the rat. Lidocaine (3 mM) decreased the glycine-induced Cl- current (Gly-ICl) more potently (to 46% of the control value) than the gamma-aminobutyric acid-induced Cl- current (GABA-ICl; to 75%), whereas the agent had little effect on the excitatory glutamate response. The reduction in the Gly-ICl was dose-dependent, with a dissociation constant (KD) of 3 mM and a Hill coefficient of 0.96. A non-competitive inhibition was suggested by a double reciprocal plot of the effects of lidocaine on the concentration-response curve of the Gly-ICl. Benzocaine, a neutral local anesthetic at physiological pH, decreased the Gly-ICl more potently than lidocaine, while QX314, a permanently charged quaternary derivative of lidocaine, produced a much smaller inhibition, thereby indicating that the neutral form of local anesthetics is more effective in reducing the Gly-ICl. The depression of the Gly-ICl and GABA-ICl in central neurons may contribute to local anesthetic-induced convulsions.