Abstract
The primary sensory neuron in the mesencephalic trigeminal nucleus (MTN) is unique in expressing various receptors including glutamate receptors (GluRs). To characterize these GluRs, we performed the whole-cell voltage-clamp recording from MTN neurons in slice preparations. At the holding potentials ranging from -110 to +90 mV, the current responses to puff application of glutamate were recorded. When the peak current amplitudes were plotted against the holding potentials, an N-shaped I-V relationship crossing near 0 mV was obtained. This N-shaped relationship was distinct from those previously seen in inwardly rectifying type II and outwardly rectifying type I AMPA channels. Furthermore, at negative holding potentials, the biphasic responses consisting of inward and outward current components were often observed. The outward component seen at < 0 mV was sensitive to Cs+ and ZD7288, indicating an involvement of h-current in generating the glutamate-induced outward current. Provided that GluR channels shared the microdomain with h-channels in MTN neurons, it is possible that the apparent reversal potential of glutamate-induced current is shifted negatively due to the co-localization of the two active channels that have different Na+/K+ permeability ratio of 0.2 and 1. Furthermore, a transient increase in [Na+]i in such a microdomain would further shift the reversal potential negatively, leading to a generation of biphasic responses where the N-shaped I-V relationship can be seen. [J Physiol Sci. 2007;57 Suppl:S232]
