Characterization of phosphorylation sites on the glutamate receptor 4 subunit of the AMPA receptors.
1. Currents in response to rapid application of glutamate and its agonists were studied in cells dissociated from the ventral spinal cord of adult rats. 2. Glutamate activated an inward current that desensitized in less than 15 ms. 3. Responses to quisqualate and to DL-alpha-amino-3-hydroxy-5-methyl-isoxeazolepropionic acid (AMPA) also desensitized with time constants ranging from 7 to 18 ms in whole cell configuration and from 3.4 to 4.3 ms in outside-out configuration. Desensitization rate was independent of membrane potential. Single-channel conductance was 12 pS. 4. Currents in response to N-methyl-D-aspartate activation also desensitized; the time constants ranged from 15 to 50 ms. Single-channel conductance was 23 pS. 5. Kainate responses did not desensitize appreciably. Single-channel conductance was 17 pS. 6. These data obtained from adult cells are similar to values reported for cultured embryonic and neonatal neurons, indicating minimal postnatal changes in these aspects of glutamate receptors.