Changes in glutamate-evoked currents of frog motoneurones by extracellular Mg2+.

Responses of frog motoneurones to glutamate were studied using a single electrode voltage clamp method. At resting membrane potential glutamate evoked biphasic effects: firstly a transient outward current with reversal potential between -90 and -100 mV. Secondly an inward current with reversal potential near 0 mV and non-linearly related to the holding potential. Mg2+ (1 mM) had no effect on the outward current but reduced the inward current and its slope conductance at holding potentials more negative than -60 mV. These data indicate that the operation of the inward current activated by glutamate was partly but not solely controlled by extracellular Mg2+.