Gorman A M, Grieve A, Griffiths R
Division of Cell and Molecular Biology, School of Biological and Medical Sciences, University of St. Andrews, Scotland, U.K.
J Neurochem. 1995 Dec;65(6):2473-83. doi: 10.1046/j.1471-4159.1995.65062473.x.
The effect of ionotropic excitatory amino acids and potassium on the formation of inositol phosphates elicited by the metabotropic glutamate receptor agonist (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (trans-ACPD) was studied in mouse cerebellar granule cells. In Mg(2+)-containing buffers, NMDA (50-100 microM), alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA; 10-1,000 microM), and high potassium (10-30 mM) enhanced synergistically the response to a maximally effective concentration of 500 microM trans-ACPD. Potentiation of the trans-ACPD response was blocked by higher concentrations of NMDA (> 500 microM) and potassium (> 35 mM) but not by AMPA (up to 1 mM). The potentiation by NMDA of the trans-ACPD-stimulated phosphoinositide hydrolysis was blocked by D,L-2-amino-5-phosphonopentanoic acid (APV), a competitive NMDA-receptor antagonist. Under Mg(2+)-free conditions, the accumulation of inositol phosphates in the presence of trans-ACPD alone was equal to that attained by trans-ACPD in Mg(2+)-containing buffers when costimulated with maximally enhancing concentrations of NMDA (50 microM). trans-ACPD potentiated synergistically the NMDA-evoked increases in cytosolic free-Ca2+ levels in Mg(2+)-containing but not in Mg(2+)-free solutions, and moreover did not enhance the AMPA-evoked increases in cytosolic free-Ca2+ levels. The calcium ionophore A23187 caused a dose-dependent increase in inositol phosphate accumulation but did not enhance the response stimulated by trans-ACPD alone. These results demonstrate the existence of cross talk between metabotropic and ionotropic glutamate receptors in cerebellar granule cells. The exact mechanism remains unclear but appears to involve interplay of G protein-coupled phospholipase C activation and regulated elevation of cytosolic free-Ca2+ levels. This study may provide a framework for future investigations at the cellular and molecular level that clarify the functional relevance and molecular mechanisms that are described.
在小鼠小脑颗粒细胞中，研究了离子型兴奋性氨基酸和钾对代谢型谷氨酸受体激动剂（±）-1-氨基环戊烷-反式-1,3-二羧酸（反式-ACPD）引发的肌醇磷酸形成的影响。在含镁（2+）的缓冲液中，N-甲基-D-天冬氨酸（NMDA，50-100微摩尔）、α-氨基-3-羟基-5-甲基-4-异恶唑丙酸（AMPA，10-1000微摩尔）和高钾（10-30毫摩尔）协同增强了对500微摩尔反式-ACPD最大有效浓度的反应。较高浓度的NMDA（>500微摩尔）和钾（>35毫摩尔）可阻断反式-ACPD反应的增强，但AMPA（高达1毫摩尔）则不能。竞争性NMDA受体拮抗剂D,L-2-氨基-5-磷酸戊酸（APV）可阻断NMDA对反式-ACPD刺激的磷酸肌醇水解的增强作用。在无镁（2+）条件下，单独存在反式-ACPD时肌醇磷酸的积累量与在含镁（2+）缓冲液中与最大增强浓度的NMDA（50微摩尔）共同刺激时反式-ACPD所达到的积累量相等。反式-ACPD在含镁（2+）但不含镁（2+）的溶液中协同增强了NMDA诱发的胞质游离钙（Ca2+）水平的升高，而且并未增强AMPA诱发的胞质游离钙（Ca2+）水平的升高。钙离子载体A23187导致肌醇磷酸积累呈剂量依赖性增加，但并未增强单独由反式-ACPD刺激的反应。这些结果表明，小脑颗粒细胞中代谢型和离子型谷氨酸受体之间存在相互作用。确切机制尚不清楚，但似乎涉及G蛋白偶联磷脂酶C激活与胞质游离钙（Ca2+）水平调节性升高之间的相互作用。本研究可能为未来在细胞和分子水平上的研究提供一个框架，以阐明所描述的功能相关性和分子机制。
