Attwell D, Wilson M, Wu S M
J Physiol. 1984 Jul;352:703-37. doi: 10.1113/jphysiol.1984.sp015318.
A quantitative description of the electrical properties of the photoreceptor layer in the salamander retina was obtained from earlier data on the characteristics of isolated rods and cones and on rod-rod coupling, and from new data on rod-cone and cone-cone coupling and on the rod photocurrent. Injecting -1 nA current into a rod elicits hyperpolarizations of about 20 mV in an adjacent rod and 4 mV in an adjacent cone. Responses of more distant receptors are smaller. Injecting -1 nA into a cone elicits hyperpolarizations of about 4 mV in an adjacent rod and 0.4 mV in a nearby cone. Depolarizing current evokes smaller responses. Assuming, in agreement with anatomical evidence, that each rod is electrically coupled to four rods and to four cones around it, and that there is no direct electrical coupling between cones, we found these results could be predicted from the properties of isolated rods and cones if adjacent rods are coupled by a resistance of 300 M omega and adjacent rods and cones are coupled by a resistance of 5000 M omega. The small cone-cone coupling seen is due to coupling via intervening rods. The two halves of double cones are not electrically coupled. The spectral sensitivity of both halves is a maximum around 620 nm wave-length. The rod photocurrent has been characterized by voltage-clamping rods isolated from the retina. In agreement with Bader, MacLeish & Schwartz (1979) we found the time course of the photocurrent to be approximately independent of voltage between -35 and -85 mV. The voltage responses of rods, single cones and double cones isolated from the retina obey the principle of univariance. Responses of receptors in the retina do not obey univariance. The main deviations from univariance observed can be explained if adjacent rods and cones are coupled by a resistance of 5000 M omega. Our data demonstrate that rod-cone coupling is relatively weak. We simplified our description of the photoreceptor network, by omitting cones, to investigate the spatiotemporal processing that the rod network is capable of. Computer simulations predict, as is found experimentally, that the rod voltage response to a large spot of bright light should show a much more pronounced initial transient hyperpolarization than the response to a small spot of light of the same intensity. This difference is produced by the combination of electrical coupling of the rods with the existence of a voltage-gated current, IA, in the rod membrane.(ABSTRACT TRUNCATED AT 400 WORDS)
根据此前关于分离的视杆细胞和视锥细胞特性以及视杆细胞 - 视杆细胞耦合的数据，以及关于视杆细胞 - 视锥细胞和视锥细胞 - 视锥细胞耦合以及视杆细胞光电流的新数据，获得了蝾螈视网膜光感受器层电特性的定量描述。向一个视杆细胞注入 -1 nA 的电流，会在相邻视杆细胞中引起约 20 mV 的超极化，在相邻视锥细胞中引起 4 mV 的超极化。距离更远的感受器的反应较小。向一个视锥细胞注入 -1 nA 的电流，会在相邻视杆细胞中引起约 4 mV 的超极化，在附近视锥细胞中引起 0.4 mV 的超极化。去极化电流引起的反应较小。与解剖学证据一致，假设每个视杆细胞与其周围的四个视杆细胞和四个视锥细胞存在电耦合，并且视锥细胞之间不存在直接电耦合，我们发现，如果相邻视杆细胞通过 300 MΩ 的电阻耦合，相邻视杆细胞和视锥细胞通过 5000 MΩ 的电阻耦合，那么这些结果可以从分离的视杆细胞和视锥细胞的特性中预测出来。观察到的较小的视锥细胞 - 视锥细胞耦合是由于通过中间视杆细胞的耦合。双视锥细胞的两半没有电耦合。两半的光谱敏感性在波长约 620 nm 处最大。视杆细胞光电流已通过对从视网膜分离的视杆细胞进行电压钳制来表征。与巴德、麦克利什和施瓦茨（1979 年）一致，我们发现光电流的时间进程在 -35 至 -85 mV 之间的电压下大致与电压无关。从视网膜分离的视杆细胞、单视锥细胞和双视锥细胞的电压反应遵循单变量原则。视网膜中感受器的反应不遵循单变量原则。如果相邻视杆细胞和视锥细胞通过 5000 MΩ 的电阻耦合，那么观察到的与单变量原则的主要偏差就可以得到解释。我们的数据表明视杆细胞 - 视锥细胞耦合相对较弱。我们通过省略视锥细胞简化了对光感受器网络的描述，以研究视杆细胞网络能够进行的时空处理。计算机模拟预测，正如实验发现的那样，视杆细胞对大光斑强光的电压反应应该比相同强度小光斑光的反应表现出更明显的初始瞬时超极化。这种差异是由视杆细胞的电耦合与视杆细胞膜中存在的电压门控电流 IA 共同产生的。（摘要截取自 400 字）
