Glutamate currents in mammalian spinal neurons: resolution of a paradox

Mouse spinal cord neurons grown in tissue culture were impaled with a pair of microelectrodes containing 1 M CsCl and voltage-clamped. Membrane currents evoked by excitatory amino acids were studied over the potential range -70 to +20 mV. Glutamate currents behaved as though generated by simultaneous activation of two conductance mechanisms, one voltage-sensitive, the other conventional. Block of NMDA receptors with the competitive antagonist 2-APV removed the voltage-sensitive component of the glutamate response. These results help to explain the paradoxical lack of conductance-change previously reported for glutamate responses recorded in the mammalian CNS.