Villanueva S, Frenz P, Dragnic Y, Orrego F
Department of Physiology and Biophysics, Faculty of Medicine, University of Chile, Santiago.
Brain Res. 1988 Oct 4;461(2):377-80. doi: 10.1016/0006-8993(88)90271-5.
The efflux of endogenous glutamate from thin slices of rat brain cortex superfused in vitro with artificial cerebrospinal fluid (ACSF) was studied. Initially, glutamate efflux was very high (2.5 nmol/mg protein/min), possibly because of the cutting procedure, but declined sharply, and at 30 min of superfusion was 25 pmol/mg protein/min. In ACSF without added calcium, spontaneous glutamate efflux was always higher than that in calcium-containing medium, e.g. at 30 min it was 75 pmol/mg protein/min. Addition of 10 microM veratridine for 2 min, between 30 and 32 min of superfusion, led, in ACSF with calcium, to an increase in glutamate efflux of 288%, when the maximum efflux following veratridine is compared to the glutamate efflux that immediately preceded the application of this drug (from 25 to 97 pmol/mg protein/min), while in ACSF without added calcium, veratridine induced an increase of only 117% (from 75 to 163 pmol/mg protein/min). These results are interpreted as due to the dual effect of veratridine. In calcium-containing ACSF, veratridine increases sodium influx which depolarizes the neurons and opens voltage-sensitive calcium channels. The increased intraneuronal calcium induces glutamate release from synaptic vesicles, while increased intracellular sodium enhances the release of soluble cytoplasmic glutamate by the reverse operation of the plasma membrane, sodium-dependent glutamate carrier. In ACSF without calcium, the release of vesicular glutamate is suppressed, while the sodium-dependent mechanism remains. This appears as if veratridine-induced glutamate efflux were only partially calcium-dependent.
研究了在体外用人造脑脊液（ACSF）灌注的大鼠大脑皮层薄片中内源性谷氨酸的流出情况。最初，谷氨酸流出量非常高（2.5 nmol/mg蛋白质/分钟），这可能是由于切割过程所致，但随后急剧下降，在灌注30分钟时为25 pmol/mg蛋白质/分钟。在未添加钙的ACSF中，自发性谷氨酸流出量总是高于含钙培养基中的流出量，例如在30分钟时为75 pmol/mg蛋白质/分钟。在灌注30至32分钟之间添加10 microM藜芦定2分钟，在含钙的ACSF中，与施用该药物前即刻的谷氨酸流出量（从25至97 pmol/mg蛋白质/分钟）相比，藜芦定导致谷氨酸流出量增加288%，而在未添加钙的ACSF中，藜芦定仅诱导增加117%（从75至163 pmol/mg蛋白质/分钟）。这些结果被解释为是由于藜芦定的双重作用。在含钙的ACSF中，藜芦定增加钠内流，使神经元去极化并打开电压敏感性钙通道。细胞内钙增加诱导谷氨酸从突触小泡释放，而细胞内钠增加通过质膜钠依赖性谷氨酸载体的反向运作增强可溶性细胞质谷氨酸的释放。在无钙的ACSF中，小泡谷氨酸的释放受到抑制，而钠依赖性机制仍然存在。这似乎表明藜芦定诱导的谷氨酸流出仅部分依赖于钙。
