Joirrnul zyxwvutsrqponmlkjih ol'Ntwuchemi.rrry zyxwvutsrqpon Raven Press, Ltd.. New York 1993 International Society for Neurochemistry zyxwvutsrqp (R, S)-a-Amino-3-Hydroxy-5 -Methylisoxazole-4-Propionic Acid (AMPA) Receptors Mediate a Calcium-Dependent Inhibition of the Metabotropic Glutamate Receptor- Stimulated Formation of Inositol 1,4,5-Trisphosphate Gyorgy Lonart, Sudarkodi Alagarsamy, and Kenneth M. Johnson Dcyurtinenl zyxwvutsrqp of Pharmacolo,q* zyxwvutsrq und To.vicologj: University ef Texas Medical Brunch. Galveston. Te.xus. USA. Abstract: L-Glutamate(3-1,000pM)and( IS,3R)-l-amino- cyclopentane- I ,3-dicarboxylic acid zyxwvutsr ( I S.3R-ACPD: 10- 1.000 pM), a selective agonist for the metabotropic gluta- mate receptor, stimulated the formation of inositol 1,4.5- trisphosphate in a concentration-dependent manner. L-Glutamate was half as efficacious as IS,3R-ACPD. N- methyl-D-aspartate (NMDA: I nM to 1 mM) did not signifi- cantly influence the response to a maximally effective con- centration of IS.3R-ACPD (100 pM). On the other hand, coapplication of (RS) zyxwvuts -a-amino-3-hydroxy-5-methylisoxa- zole-4-propionic acid (AMPA: 1-300 nbf) produced a con- centration- and time-dependent inhibition of the 1S.3R- ACPD effect. with a maximal inhibition (97%) at 100 nM. Ten micromolar 6-cyano-7-nitroquinoxaline-2.3-dione. an antagonist of the AMPA receptor, blocked the inhibitory effect of AMPA. Reduced extracellular calcium concentra- tion. as well as 10 pM nimodipine, an L-type calcium chan- nel antagonist, inhibited the AMPA influence on the IS.3R- ACPD response. W-7, a calcium/calmodulin antagonist, prevented the inhibition by AMPA. whereas H-7. an inhibi- tor of protein kinase C, had no effect. These data suggest that activation of AMPA receptors has an inhibitory influ- ence on inositol 1.4.5-trisphosphate formation mediated by stimulation of the metabotropic glutamate receptor. The mechanism of action involves calcium influx through L- type calcium channels and possible activation of calcium/calmodulin-dependent enzymes. Key Words: 1 -Aminocyclopentane- 1.3-dicarboxylic acid-Desensitiza- tion-H-7-Hippocampus-Ar-Methyl-~aspartate-W-7. Lonart G. zyxwv et al. (R.S)-ru-Amino-3-hydroxy-5-methylisoxa- zole-4-propionic acid (AMPA) receptors mediate a calcium- dependent inhibition of the metabotropic glutamate recep- tor-stimulated formation of inositol 1,4,5-trisphosphate. J. Neurochern. 60, 1739- 1745 ( 1993). Glutamate is a major excitatory neurotransmitter in the mammalian CNS. The ionotropic glutamate receptors open nonselective cation channels, whereas the metabotropic receptors stimulate or inhibit sec- ond messenger systems (Tanabe et al., 1992). The ex- tent of interactions between these receptor types is a matter of great current interest. Several recent studies indicate that the sensitivity of ionotropic or metabo- tropic glutamate receptors can be modified by phos- phorylation or dephosphorylation. For example. whole-cell recordings from cultured neurons showed that the N-methyla-aspartate (NMDA)-induced ion current was dependent on the availability of ATP (Mody et al., 1988). a phosphate donor of protein phosphorylation by protein kinases. In spinal cord slices, direct activation of protein kinase C with phor- bol esters (Gerber et al., 1989) or indirect stimulation of this enzyme with a p-opioid agonist induced an increase in the NMDA receptor-mediated response (Chen and Huang. 199 1). Interestingly, activation of protein kinase C by phorbol esters inhibits the meta- botropic glutamate receptor (Manzoni et al.. 1991 ). Also. in a striatal cell culture preparation. glutamate pretreatment induced desensitization of the metabo- tropic response. This was reduced by inhibitors of protein kinases (Catania et al.. 1991). ~ Received July 3. 1991: revised manuscript received October I. methylisoxazole-J-propionic acid: CaM. calcium/calmodulin: CNQN. 6-c!ano-7-nitroquino~aline-2.3-dione: H-7. 145-isoquin- Address correspondence and reprint requests to Dr. K. M. John- olinesulfon! I)-2-meth! Ipiperarine: Ins( I .4.5)P,. inositol I .J.5- trisphosphate: Ins( I .3.4.5)P4. inositol I .3.4.5-tetrakisphosphate: NMDA. .A'-methyl-D+aspartdte: TCA. trichloroacetic acid: W-7. zy K-( 6-arninohexyl)-5-chloro- 1 -naphthalenesulfonarnide. 1992: accepted October 12. 1992. son at Department of Pharmacology and Toxicology, University of Texas Medical Branch. Galveston. TX 77555-103 I, U.S.A. .-lhhrei~iurrons iwd; I S.3R-ACPD. ( I S.3R)- I -arninocyclopen- tane-1.3-dicarboxylic acid: AMPA. (R.S)-n-amino-3-hydroxy-5- I739