Chrachri Abdesslam, Nelson Lisa, Williamson Roddy
School of Biological Sciences, University of Plymouth, UK.
Vis Neurosci. 2005 May-Jun;22(3):359-70. doi: 10.1017/S0952523805223106.
A new tissue slice preparation of the cuttlefish eye is described that permits patch-clamp recordings to be acquired from intact photoreceptors during stimulation of the retina with controlled light flashes. Whole-cell recordings using this preparation, from the retinas of very young Sepia officinalis demonstrated that the magnitude, latency, and kinetics of the flash-induced photocurrent are closely dependent on the magnitude of the flash intensity. Depolarizing steps to voltages more positive than -40 mV, from a membrane holding potential of -60 mV, induced a transient inward current followed by a larger, more sustained outward current in these early-stage photoreceptors. The latter current resembled the delayed rectifier (I(K)) already identified in many other nerve cells, including photoreceptors. This current was activated at -30 mV from a holding potential of -60 mV, had a sustained time course, and was blocked in a dose-dependent manner by tetraethylammonium chloride (TEA). The smaller, transient, inward current appeared at potentials more positive than -50 mV, reached peak amplitude at -30 mV and decreased with further depolarization. This current was characterized as the sodium current (I(Na)) on the basis that it was inactivated at holding potentials above -40 mV, was blocked by tetrodotoxin (TTX) and was insensitive to cobalt. Intracellular perfusion of the photoreceptors, via the patch pipette, demonstrated that U-73122 and heparin blocked the evoked photocurrent in a dose-dependent manner, suggesting the involvement of the phospholipase C (PLC) and inositol 1,4,5-triphosphate (InsP(3)), respectively, in the phototransduction cascade. Perfusion with cyclic GMP increased significantly the evoked photocurrent, while the inclusion of phorbol-12,13-dibutyrate reduced significantly the evoked photocurrent, supporting the involvement of cGMP and the diacylglycerol (DAG) pathways, respectively, in the cuttlefish transduction process.
本文描述了一种新的乌贼眼组织切片制备方法，该方法允许在使用可控光闪光刺激视网膜时，从完整的光感受器获取膜片钳记录。使用这种制备方法对非常年幼的乌贼（Sepia officinalis）视网膜进行全细胞记录，结果表明闪光诱导的光电流的幅度、潜伏期和动力学密切依赖于闪光强度的大小。从 -60 mV 的膜钳制电位向比 -40 mV 更正的电压进行去极化步骤，在这些早期光感受器中诱导出一个短暂的内向电流，随后是一个更大、更持续的外向电流。后一种电流类似于在许多其他神经细胞（包括光感受器）中已经鉴定出的延迟整流器（I(K)）。该电流在从 -60 mV 的钳制电位到 -30 mV 时被激活，具有持续的时间进程，并被氯化四乙铵（TEA）以剂量依赖性方式阻断。较小的、短暂的内向电流出现在比 -50 mV 更正的电位下，在 -30 mV 时达到峰值幅度，并随着进一步去极化而减小。基于该电流在高于 -40 mV 的钳制电位下失活、被河豚毒素（TTX）阻断且对钴不敏感，将其表征为钠电流（I(Na)）。通过膜片吸管对光感受器进行细胞内灌注表明，U - 73122 和肝素以剂量依赖性方式阻断诱发的光电流，这分别表明磷脂酶 C（PLC）和肌醇 1,4,5 - 三磷酸（InsP(3)）参与了光转导级联反应。用环鸟苷酸（cGMP）灌注可显著增加诱发的光电流，而加入佛波醇 - 12,13 - 二丁酸酯可显著降低诱发的光电流，这分别支持了 cGMP 和二酰基甘油（DAG）途径参与乌贼光转导过程。
