Na(+)-Ca2+ exchanger-associated membrane currents were studied in cultured murine neocortical neurons, using whole-cell recording combined with intracellular perfusion. A net inward current specifically associated with forward (Na+(o)-Ca2+(i)) exchange was evoked at -40 mV by switching external 140 mM Li+ to 140 mM Na+. The voltage dependence of this current was consistent with that predicted for 3Na+1Ca2+ exchange. As expected, the current depended on internal Ca2+, and could be blocked by intracellular application of the exchanger inhibitory peptide, XIP. Raising internal Na+ from 3 to 20 mM or switching the external solution from 140 mM Li+ to 30 mM Na+ activated outward currents, consistent with reverse (Na+(i)-Ca2+(o)) exchange. An external Ca2(+)-sensitive current was also identified as associated with reverse Na(+)-Ca2+ exchange based on its internal Na+ dependence and sensitivity to XIP. Combined application of external Na+ and Ca2+ in the absence of internal Na+ triggered a 3.3-fold larger inward current than the current activated in the presence of 3 mM internal Na+, raising the intriguing possibility that Na(+)-Ca2+ exchangers might concurrently operate in both the forward and the reverse direction, perhaps in different subcellular locations. With this idea in mind, we examined the effect of excitotoxic glutamate receptor activation on exchanger operation. After 3-5 min of exposure to 100-200 microM glutamate, the forward exchanger current was significantly increased even when external Na+ was reduced to 100 mM, and the external Ca2(+)-activated reverse exchanger current was eliminated.

译文

使用全细胞记录结合细胞内灌注,在培养的鼠新皮层神经元中研究了Na ()-Ca2交换剂相关的膜电流。通过将外部140 mM Li切换到140 mM Na,在40 mV时诱发了与正向 (Na (o)-Ca2 (i)) 交换特别相关的净向内电流。该电流的电压依赖性与3Na 1Ca2交换的预测一致。如预期的那样,电流取决于内部Ca2,并且可以通过在细胞内应用交换抑制肽XIP来阻断电流。将内部Na + 从3升高到20 mm或将外部溶液从140 mM Li + 切换到30mm Na + 激活的外向电流,与反向 (Na +(i)-Ca2 +(o)) 交换一致。根据其内部Na依赖性和对XIP的敏感性,还确定了对外部Ca2 () 敏感的电流与反向Na ()-Ca2交换有关。在不存在内部Na的情况下组合施加外部Na和Ca2触发的内向电流比在3毫米内部Na存在下激活的电流大3.3倍,提出了Na ()-Ca2交换剂可能同时在正向和反向同时运行的有趣可能性,也许在不同的亚细胞位置。考虑到这一想法,我们研究了兴奋性谷氨酸受体激活对交换器操作的影响。暴露于100-200 microM谷氨酸3-5分钟后,即使外部Na降低到100 mM,正向交换电流也显着增加,并且消除了外部Ca2 () 激活的反向交换电流。

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