Rego A C, Agostinho P, Melo J, Cunha R A, Oliveira C R
Center for Neurosciences of Coimbra, University of Coimbra, Portugal.
Exp Eye Res. 2000 May;70(5):577-87. doi: 10.1006/exer.1999.0815.
The role of endogenous extracellular adenosine as a tonic modulator of the extracellular accumulation of excitatory amino acids (glutamate and aspartate) caused by metabolic inhibition was investigated in cultured retinal cells. The selective adenosine A2A receptor antagonist, 4-[2-[7-amino-2-(2-furyl)(1,2,4)-triazin-5-ylamino]-ethyl]ph enol (ZM241385) (50 nM), increased the release of glutamate (three- to four-fold) and of aspartate (nearly two-fold) upon iodoacetic acid-induced glycolysis inhibition, in the presence or in the absence of Ca2+. Blockade of tonic activation of A2A receptors by ZM241385 also increased (nearly two-fold) the ischemia-induced release of glutamate and aspartate. Furthermore, another selective A2A receptor antagonist, 5-amino-7-(2-phenylethyl)-2-(2-furyl)pyrazolo[4,3-e]-1,2,4-triazolo[1,5- c] pyrimidine (SCH58261), also increased the release of aspartate and glutamate by about two-fold in cells submitted to glycolysis inhibition. In contrast, the selective adenosine A1 receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) (100 nM), did not significantly modify the extracellular accumulation of either glutamate or aspartate caused by inducers of chemical ischemia or glycolytic inhibitors. Inhibition of glycolysis also increased (about three-fold) the extracellular accumulation of GABA, which was virtually unchanged by ZM241385. Furthermore, the GABAA receptor antagonist, bicuculline (10 microM), only increased (nearly two-fold) the iodoacetic acid-induced Ca(2+)-dependent release of glutamate, whereas the GABAB receptor antagonist, 3-aminopropyl(diethoxymethyl) phosphinic acid, CGP35348 (100 microM), was devoid of effects on the extracellular accumulation of glutamate and aspartate. These results show that endogenous extracellular adenosine, which rises under conditions of inhibited glycolysis, tonically inhibits the extracellular accumulation of excitatory amino acid through the activation of A2A, but not A1, adenosine receptors, and this effect is independent of GABAA and GABAB functions in the cultured retinal cells.
在培养的视网膜细胞中，研究了内源性细胞外腺苷作为代谢抑制引起的兴奋性氨基酸（谷氨酸和天冬氨酸）细胞外积累的一种紧张性调节剂的作用。选择性腺苷A2A受体拮抗剂4-[2-[7-氨基-2-(2-呋喃基)(1,2,4)-三嗪-5-基氨基]-乙基]苯酚（ZM241385）（50 nM），在存在或不存在Ca2+的情况下，在碘乙酸诱导的糖酵解抑制时，增加了谷氨酸（三到四倍）和天冬氨酸（近两倍）的释放。ZM241385对A2A受体紧张性激活的阻断也增加了（近两倍）缺血诱导的谷氨酸和天冬氨酸的释放。此外，另一种选择性A2A受体拮抗剂5-氨基-7-(2-苯乙基)-2-(2-呋喃基)吡唑并[4,3-e]-1,2,4-三唑并[1,5-c]嘧啶（SCH58261），在糖酵解抑制的细胞中也使天冬氨酸和谷氨酸的释放增加了约两倍。相反，选择性腺苷A1受体拮抗剂1,3-二丙基-8-环戊基黄嘌呤（DPCPX）（100 nM），并没有显著改变化学缺血诱导剂或糖酵解抑制剂引起的谷氨酸或天冬氨酸的细胞外积累。糖酵解抑制也增加了（约三倍）GABA的细胞外积累，而ZM241385对其几乎没有影响。此外，GABAA受体拮抗剂荷包牡丹碱（10 microM），仅增加了（近两倍）碘乙酸诱导的Ca(2+)依赖性谷氨酸释放，而GABAB受体拮抗剂3-氨基丙基(二乙氧基甲基)次膦酸，CGP-35348（100 microM），对谷氨酸和天冬氨酸的细胞外积累没有影响。这些结果表明，在糖酵解抑制条件下升高的内源性细胞外腺苷，通过激活A2A而不是A1腺苷受体，紧张性地抑制兴奋性氨基酸在细胞外的积累，并且这种作用在培养的视网膜细胞中独立于GABAA和GABAB的功能。
