Utilization of the resolved L-isomer of 2-amino-6-phosphonohexanoic acid (L-AP6) as a selective agonist for a quisqualate-sensitized site in hippocampal CA1 pyramidal neurons.
Brief exposure of rat hippocampal slices to quisqualic acid (QUIS) sensitizes neurons to depolarization by the alpha-amino-omega-phosphonate excitatory amino acid (EAA) analogues AP4, AP5 and AP6. These phosphonates interact with a novel QUIS-sensitized site. Whereas L-AP4 and D-AP5 cross-react with other EAA receptors, DL-AP6 has been shown to be relatively selective for the QUIS-sensitized site. This specificity of DL-AP6, in conjunction with the apparent preference of this site for L-isomers, suggested that the hitherto unavailable L-isomer of AP6 would be a potent and specific agonist. We report the resolution of the D- and L-enantiomers of AP6 by fractional crystallization of the L-lysine salt of DL-AP6. We also report the pharmacological responses of kainate/AMPA, NMDA, lateral perforant path L-AP4 receptors and the CA1 QUIS-sensitized site to D- and L-AP6, and compare these responses to the D- and L-isomers of AP3, AP4, AP5 and AP7. The D-isomers of AP4, AP5 and AP6 were 5-, 3- and 14-fold less potent for the QUIS-sensitized site than their respective L-isomers. While L-AP4 and L-AP5 cross-reacted with NMDA and L-AP4 receptors, L-AP6 was found to be highly potent and specific for the QUIS-sensitized site (IC50 = 40 microM). Its IC50 values for kainate/AMPA, NMDA and L-AP4 receptors were > 10, 3 and 0.8 mM, respectively. As with AP4 and AP5, sensitization to L-AP6 was reversed by L-alpha-aminoadipate.
Department of Biochemistry, Medical School, University of Minnesota, Minneapolis 55455-0347.
M K
MK
Schulte
R J
RJ
Roon
D J
DJ
Chalmers
D C
DC
Sunter
J F
JF
Koerner
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000818:Animals; D005071:Evoked Potentials / Q000187:drug effects; D005110:Extracellular Space / Q000502:physiology; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D009434:Neural Pathways / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D009646:Norleucine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D017966:Pyramidal Cells / Q000187:drug effects / Q000378:metabolism*; D016318:Quisqualic Acid / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018091:Receptors, AMPA / Q000819:agonists*; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects; D013237:Stereoisomerism
D018091:Receptors, AMPA; D016194:Receptors, N-Methyl-D-Aspartate; D015763:2-Amino-5-phosphonovalerate; C043094:2-amino-6-phosphonohexanoic acid; D009646:Norleucine; D016318:Quisqualic Acid