Physiological analyses of voltage-gated ion channels and their molecular identifications in sensory neurons.

所有脊椎动物的光感受器，包括人类的光感受器，都以分级的超极化对光刺激作出反应，并且通常被认为是非尖峰神经元。为了研究人类光感受器是否能诱发动作电位，我们用全细胞膜片钳技术研究了手术切除的人类视网膜。在手术过程中，从视网膜脱离患者身上切除一小片（直径小于1 mm）视网膜，以重新连接视网膜。所有实验均按照赫尔辛基宣言的指导原则进行，并得到我们研究所伦理委员会的批准。我们发现光感受器表达电压门控Na^+通道，并在膜去极化时产生Na^+动作电位。这表明，钠尖峰可能会引起在一个明亮的光刺激的终止。钠动作电位将用于放大神经递质的释放在突然偏移的明亮light.We的光信号，从而选择性地放大“关”的一部分，还研究了是否人杆光感受器表达超极化激活的阳离子电流（Ih）。用3 mM Cs^+（一种Ih的阻断剂）可显著降低由超极化引起的慢内向电流。水浴中加入3 mM Cs^+也阻断了稳定的内向电流。我们的研究结果表明，Ih在明亮照明产生的大超极化过程中被激活，并可能修改光电压的波形。人类的视觉是相当强大的，视觉闪烁很少经历。在电流钳条件下，Cs^+、Tl^+和ZD 7288对h电流的阻断使视锥细胞和视杆细胞的静息电位超极化10-15 mV，并令人惊讶地产生了自发性动作电位。我们认为，h电流可能通过抑制人类视锥细胞和视杆细胞中自发Na^+峰的产生而有助于防止视觉闪烁。

All vertebrate photoreceptors, including those of humans, respond to light stimuli with a graded hyperpolarization, and are commonly thought to be non-spiking neurons. To examine whether human photoreceptors can elicit action potentials, we studied surgically excised human retina using the whole-cell patch-clamp recording technique. A small piece (diameter less than 1 mm) of retina was excised from patients with retinal detachment during the surgical procedure to re-attach the retina. All experiments were performed in compliance with the guideline of the Declaration of Helsinki and approved by the ethics committee of our institute. We found that photoreceptors express voltage-gated Na^+ channels, and generate Na^+ action potentials in response to membrane de polarization. This suggests that Na spikes might be elicited at the termination of a bright light stimulus. The Na action potentials would serve to amplify the release of neurotransmitter at the sudden offset of a bright light, and thus selectively amplify the "OFF" part of the light signal.We also examined whether human rod photoreceptors express hyperpolarization-activated cationic currents (Ih). The slow inward current induced by hyperpolarization was markedly reduced by bath application of 3 mM Cs^+, a blocker of Ih,. Bath application of 3 mM Cs^+ also blocked the steady inward current. Our findings suggest that Ih becomes activated during large hyperpolarizations generated by bright illumination and may modify the waveform of the photovoltage.The sense of vision in humans is quite robust and visual flickering is rarely experienced. Under current-clamp conditions, blockage by Cs^+, Tl^+ and ZD7288 of an h current hyperpolarized the resting potentials of cones and rods by 〜10-15 mV, and surprisingly generated spontaneous action potentials. We suggest that the h current may contribute to preventing visual flickering by inhibiting the generation of spontaneous Na^+ spikes in human cones and rods.