The Journal of Neurophysiology Vol. 83 No. 1 January 2000, pp. 50-59
Copyright ©2000 by the American Physiological Society

Contribution of Ca²⁺-Permeable AMPA/KA Receptors to Glutamate-Induced Ca²⁺ Rise in Embryonic Lumbar Motoneurons In Situ

 ¹II. Physiologisches Institut, Universität Göttingen, D-37073 Gottingen; and  ²Klinische Forschergruppe Neuroregeneration, Neurologische Klinik, Universität Würzburg, D-97080 Wurzburg, Germany

Metzger, Friedrich, Anna Kulik, Michael Sendtner, and Klaus Ballanyi. Contribution of Ca²⁺-Permeable AMPA/KA Receptors to Glutamate-Induced Ca²⁺ Rise in Embryonic Lumbar Motoneurons In Situ. J. Neurophysiol. 83: 50-59, 2000. Intracellular Ca²⁺ ([Ca²⁺]_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 µM to 1 mM) evoked a [Ca²⁺]_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--amino-3-hydroxy-5-methyl-4-isoxalone (S-AMPA) evoked a similar [Ca²⁺]_i transient as glutamate. N-methyl-D-aspartate (NMDA) was only effective to increase [Ca²⁺]_i in Mg²⁺-free saline, whereas [1S,3R]-1-aminocyclopentane-1,3-dicarboxylic acid ([1S,3R]-ACPD) had no effect. The glutamate-induced [Ca²⁺]_i rise was suppressed in Ca²⁺-free superfusate. Depletion of Ca²⁺ stores with cyclopiazonic acid (CPA) did not affect the response. Thirty-six percent of the [Ca²⁺]_i increase in response to membrane depolarization induced by a 50 mM K⁺ solution persisted on combined application of the voltage-gated Ca²⁺ channel blockers nifedipine, -conotoxin-GVIA and -agatoxin-IVA. In fura-2 dialyzed motoneurons, the glutamate-induced [Ca²⁺]_i increase was attenuated by ~70% after changing from current to voltage clamp. Forty percent of the remaining [Ca²⁺]_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 Ca²⁺ channels, including a major portion of R-type channels, constitute the predominant component of glutamate-induced [Ca²⁺]_i rises. NMDA and Ca²⁺-permeable KA/AMPA receptors contribute about equally to the remaining component of the Ca²⁺ rise. The results substantiate previous assumptions that Ca²⁺ influx through JSTX-sensitive KA/AMPA receptors is involved in (trophic) signaling in developing motoneurons.