Contribution of Ca(2+)-permeable AMPA/KA receptors to glutamate-induced Ca(2+) rise in embryonic lumbar motoneurons in situ.
Intracellular Ca(2+) ([Ca(2+)](i)) was fluorometrically measured with fura-2 in lumbar motoneurons of acutely isolated spinal cord slices from embryonic rats. In ester-loaded cells, bath-applied glutamate (3 microM to 1 mM) evoked a [Ca(2+)](i) increase by up to 250 nM that was abolished by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) plus 2-amino-5-phosphonovalerate (APV). CNQX or APV alone reduced the response by 82 and 25%, respectively. The glutamatergic agonists kainate (KA), quisqualate (QUI), and S-alpha-amino-3-hydroxy-5-methyl-4-isoxalone (S-AMPA) evoked a similar [Ca(2+)](i) transient as glutamate. N-methyl-D-aspartate (NMDA) was only effective to increase [Ca(2+)](i) in Mg(2+)-free saline, whereas [1S,3R]-1-aminocyclopentane-1,3-dicarboxylic acid ([1S,3R]-ACPD) had no effect. The glutamate-induced [Ca(2+)](i) rise was suppressed in Ca(2+)-free superfusate. Depletion of Ca(2+) stores with cyclopiazonic acid (CPA) did not affect the response. Thirty-six percent of the [Ca(2+)](i) increase in response to membrane depolarization induced by a 50 mM K(+) solution persisted on combined application of the voltage-gated Ca(2+) channel blockers nifedipine, omega-conotoxin-GVIA and omega-agatoxin-IVA. In fura-2 dialyzed motoneurons, the glutamate-induced [Ca(2+)](i) increase was attenuated by approximately 70% after changing from current to voltage clamp. Forty percent of the remaining [Ca(2+)](i) transient and 20% of the concomitant inward current of 0.3 nA were blocked by Joro spider toxin-3 (JSTX). The results show that voltage-gated Ca(2+) channels, including a major portion of R-type channels, constitute the predominant component of glutamate-induced [Ca(2+)](i) rises. NMDA and Ca(2+)-permeable KA/AMPA receptors contribute about equally to the remaining component of the Ca(2+) rise. The results substantiate previous assumptions that Ca(2+) influx through JSTX-sensitive KA/AMPA receptors is involved in (trophic) signaling in developing motoneurons.
Metzger
F
F
Klinische Forschergruppe Neuroregeneration, Neurologische Klinik, Universität Würzburg, D-97080 Wurzburg, Germany.
Kulik
A
A
Sendtner
M
M
Ballanyi
K
K
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D003515:Cycloleucine / Q000031:analogs & derivatives / Q000494:pharmacology; D004622:Embryo, Mammalian; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D018698:Glutamic Acid / Q000494:pharmacology; D066298:In Vitro Techniques; D007608:Kainic Acid / Q000494:pharmacology; D008161:Lumbosacral Region; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D009498:Neurotoxins / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D018091:Receptors, AMPA / Q000502:physiology*; D018092:Kainic Acid Receptors / Q000502:physiology*; D013111:Spider Venoms / Q000494:pharmacology; D013116:Spinal Cord / Q000196:embryology / Q000502:physiology*; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000494:pharmacology
D015763:2-Amino-5-phosphonovalerate; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D002118:Calcium; D002121:Calcium Channel Blockers; D003515:Cycloleucine; D018691:Excitatory Amino Acid Antagonists; D018698:Glutamic Acid; D007608:Kainic Acid; D009498:Neurotoxins; D018091:Receptors, AMPA; D018092:Kainic Acid Receptors; D013111:Spider Venoms; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; C044936:JSTX spider toxin; C036361:1-amino-1,3-dicarboxycyclopentane