일차 배양 해마신경세포에서 NMDA- 및 Glutamate- 유도전류의 특성

Characteristics of NMDA- and Glutamate-Induced Currents in Primary Cultured Rat Hippocampal Neurons

Objectives : This study was performed in cultured rat hippocampal neurons to investigate the acute electrophysiological features of ionotropic glutamate receptors which act as a major excitatory neurotransmitter in mammalian brain. Method : Glutamate receptor agonists were applied into the bath solution embedding in whole-cell patch-clamp recording of single hippocampal neuron. Results : In voltage-clamped at -60mV and the presence of 1mmol $Mg^{2+}$, extracellulary applied NMDA did not induce any inward current. Both the elimination of $Mg^{2+}$ and addition of glycine in bath, however, elicited a NMDAinduced inward current. $Mg^{2+}$ block current was increased gradually in more negative potentials from -30mV, showing a negative slope in I-V plot with $Mg^{2+}$. Glutamate-induced current represented an outward rectification. A non-NMDA receptor component occupied about 40% of glutamate-induced current in the voltage range of -80mV to +60mV. Conclusion : Present study suggests that glutamate activates acutely the non-NMDA receptors which induces an inward current in the level of resting membrane potential. This makes the membrane potential increase and can activate the NMDA receptors that permit calcium influx against $Mg^{2+}$ block. At the depolarized state of neuron, there may be recovery mechanisms of membrane potential to repolarize irrespective of voltage-dependent potassium channels in the hippocampal neurons.