Characterization of excitatory amino acid receptors expressed by embryonic chick motoneurons in vitro.
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)
D015763:2-Amino-5-phosphonovalerate; D000818:Animals; D001224:Aspartic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D002478:Cells, Cultured; D002642:Chick Embryo; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D018691:Excitatory Amino Acid Antagonists; D005971:Glutamates / Q000378:metabolism; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology; D007608:Kainic Acid / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009046:Motor Neurons / Q000187:drug effects* / Q000502:physiology; D016202:N-Methylaspartate; D010069:Oxadiazoles / Q000494:pharmacology; D016318:Quisqualic Acid; D017470:Receptors, Glutamate; D017981:Receptors, Neurotransmitter / Q000187:drug effects* / Q000378:metabolism; D013116:Spinal Cord / Q000187:drug effects* / Q000502:physiology; D014633:Valine / Q000031:analogs & derivatives / Q000494:pharmacology
D018691:Excitatory Amino Acid Antagonists; D005971:Glutamates; D007473:Ion Channels; D010069:Oxadiazoles; D017470:Receptors, Glutamate; D017981:Receptors, Neurotransmitter; D001224:Aspartic Acid; D016202:N-Methylaspartate; D015763:2-Amino-5-phosphonovalerate; D016318:Quisqualic Acid; D014633:Valine; D007608:Kainic Acid