Yau K W, Nakatani K
Nature. 1984;311(5987):661-3. doi: 10.1038/311661a0.
Previous work has suggested that a Na-Ca exchanger may have a key role in visual transduction in retinal rods. This exchanger is thought to maintain a low internal free Ca2+ concentration in darkness and to contribute to the rod's recovery after light by removing any internally released Ca2+. Little else is known about this transport mechanism in rods. We describe here an inward membrane current recorded from single isolated rods which appears to be associated with such external Na+-dependent Ca2+ efflux activity. External Na+, but not Li+, could generate this current; high external K+ inhibited it while small amounts of La3+ (10 microM) completely abolished it. The exchanger can also transport Sr2+, but not Ba2+ or other divalent cations. The exchange ratio was estimated to be 3Na+:1Ca2+. As well as demonstrating clearly the Na-Ca exchanger in the rod outer segment, our experiments also cast serious doubt on the commonly held view that light simply releases internal Ca2+ to bind to and block the light-sensitive conductance.
先前的研究表明，钠钙交换体可能在视网膜视杆细胞的视觉转导中起关键作用。这种交换体被认为在黑暗中维持细胞内低游离钙离子浓度，并通过清除任何细胞内释放的钙离子来促进视杆细胞在光照后的恢复。关于视杆细胞中这种转运机制，人们所知甚少。我们在此描述了从单个分离的视杆细胞记录到的内向膜电流，它似乎与这种依赖外部钠离子的钙离子外流活动有关。外部钠离子而非锂离子能产生这种电流；高外部钾离子会抑制它，而少量的镧离子（$10\ \mu M$）能完全消除它。该交换体也能转运锶离子，但不能转运钡离子或其他二价阳离子。交换比率估计为$3$个钠离子:$1$个钙离子。除了清楚地证明视杆细胞外段存在钠钙交换体外，我们的实验也对普遍认为的光只是释放细胞内钙离子以结合并阻断光敏感电导的观点提出了严重质疑。
