Journal of Neuroscience, Vol 6, 3275-3283, Copyright © 1986 by Society for Neuroscience
Characterization of excitatory amino acid receptors expressed by embryonic chick motoneurons in vitro
RJ O'Brien and GD Fischbach
We have examined the effect of L-glutamate and other excitatory amino acids
on embryonic chick motoneurons maintained in cell culture along with other
types of spinal cord cells. When the motoneuron membrane is clamped at -50
mV, glutamate induces a dose-dependent inward current. Although the
dose-response curve is hyperbolic with an ED50 of 78 microM, glutamate
apparently activates 2 types of receptors on motoneurons. The first, G1, is
activated by N-methyl-D-aspartate (NMDA) and aspartate and inhibited by
2-amino-5-phosphonovaleric acid (2-APV). The second, G2, is activated by
kainate and quisqualate and is not inhibited by 2-APV. At -50 mV, 38% of
the glutamate current is due to activation of G1 receptors and the
remaining 62% to G2 activation. In contrast to motoneurons grown with other
spinal cord cells, sorted motoneurons grown in isolation apparently exhibit
only G2 receptor- mediated currents. Both G1 and G2 currents reverse
polarity between -10 and -5 mV. However, they could be distinguished when
the membrane was hyperpolarized. G2 currents increased but G1 currents
decreased when the membrane potential was increased beyond -50 mV.
Consistent with the mixed agonist action of glutamate, glutamate currents
remained nearly constant on hyperpolarization. No evidence was obtained
that the G2 class of receptors on motoneurons could be subdivided:
Quisqualate and kainate apparently compete for the same sites;
gamma-glutamylglycine blocked quisqualate as effectively as it blocked
kainate currents when the different potencies of the 2 agonists were taken
into account.(ABSTRACT TRUNCATED AT 250 WORDS)
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