Country Michael W, Campbell Benjamin F N, Jonz Michael G
Department of Biology, University of Ottawa, Ottawa, Ontario, Canada.
J Neurophysiol. 2019 Dec 1;122(6):2284-2293. doi: 10.1152/jn.00240.2019. Epub 2019 Oct 9.
Horizontal cells (HCs) are interneurons of the outer retina that undergo graded changes in membrane potential during the light response and provide feedback to photoreceptors. We characterized spontaneous Ca-based action potentials (APs) in isolated goldfish () HCs with electrophysiological and intracellular imaging techniques. Transient changes in intracellular Ca concentration ([Ca]) were observed with fura-2 and were abolished by removal of extracellular Ca or by inhibition of Ca channels by 50 µM Cd or 100 µM nifedipine. Inhibition of Ca release from stores with 20 µM ryanodine or 50 µM dantrolene abolished Ca transients and increased baseline [Ca]. This increased baseline was prevented by blocking L-type Ca channels with nifedipine, suggesting that Ca-induced Ca release from stores may be needed to inactivate membrane Ca channels. Caffeine (3 mM) increased the frequency of Ca transients, and the store-operated channel antagonist 2-aminoethyldiphenylborinate (100 μM) counteracted this effect. APs were detected with voltage-sensitive dye imaging (FluoVolt) and current-clamp electrophysiology. In current-clamp recordings, regenerative APs were abolished by removal of extracellular Ca or in the presence of 5 mM Co or 100 µM nifedipine, and APs were amplified with 15 mM Ba. Collectively, our data suggest that during APs Ca enters through L-type Ca channels and that Ca stores (gated by ryanodine receptors) contribute to the rise in [Ca]. This work may lead to further understanding of the possible role APs have in vision, such as transitioning from light to darkness or modulating feedback from HCs to photoreceptors. Horizontal cells (HCs) are interneurons of the outer retina that provide inhibitory feedback onto photoreceptors. HCs respond to light via graded changes in membrane potential. We characterized spontaneous action potentials in HCs from goldfish and linked action potential generation to a rise in intracellular Ca via plasma membrane channels and ryanodine receptors. Action potentials may play a role in vision, such as transitioning from light to darkness, or in modulating feedback from HCs to photoreceptors.
水平细胞（HCs）是视网膜外层的中间神经元，在光反应期间其膜电位会发生分级变化，并向光感受器提供反馈。我们使用电生理和细胞内成像技术对分离的金鱼HCs中的自发钙基动作电位（APs）进行了表征。用fura-2观察到细胞内钙浓度（[Ca]）的瞬时变化，通过去除细胞外钙或用50μM镉或100μM硝苯地平抑制钙通道可消除这种变化。用20μM兰尼碱或50μM丹曲林抑制钙从储存库中的释放可消除钙瞬变并增加基线[Ca]。硝苯地平阻断L型钙通道可防止这种基线升高，这表明可能需要钙诱导的钙从储存库中释放来使膜钙通道失活。咖啡因（3 mM）增加了钙瞬变的频率，而储存库操纵通道拮抗剂2-氨基乙基二苯基硼酸盐（100μM）可抵消这种作用。用电压敏感染料成像（FluoVolt）和电流钳电生理检测到了动作电位。在电流钳记录中，去除细胞外钙或在存在5 mM钴或100μM硝苯地平的情况下可消除再生性动作电位，并用15 mM钡可放大动作电位。总的来说，我们的数据表明，在动作电位期间，钙通过L型钙通道进入，并且钙储存库（由兰尼碱受体门控）导致[Ca]升高。这项工作可能有助于进一步了解动作电位在视觉中的可能作用，例如从明适应到暗适应的转变或调节从水平细胞到光感受器的反馈。水平细胞（HCs）是视网膜外层的中间神经元，它们对光感受器提供抑制性反馈。水平细胞通过膜电位的分级变化对光作出反应。我们对金鱼水平细胞中的自发动作电位进行了表征，并将动作电位的产生与通过质膜通道和兰尼碱受体导致的细胞内钙升高联系起来。动作电位可能在视觉中发挥作用，例如从明适应到暗适应的转变，或在调节从水平细胞到光感受器的反馈中发挥作用。
