Bacigalupo J, Chinn K, Lisman J E
J Gen Physiol. 1986 Jan;87(1):73-89. doi: 10.1085/jgp.87.1.73.
The light-activated conductance of Limulus ventral photoreceptors was studied using the patch-clamp technique. Channels (40 pS) were observed whose probability of opening was greatly increased by light. In some cells the latency of channel activation was nearly the same as that of the macroscopic response, while in other cells the channel latency was much greater. Like the macroscopic conductance, channel activity was reduced by light adaptation but enhanced by the intracellular injection of the calcium chelator EGTA. The latter observation indicates that channel activation was not a secondary result of the light-induced rise in intracellular calcium. A two-microelectrode voltage-clamp method was used to measure the voltage dependence of the light-activated macroscopic conductance. It was found that this conductance is constant over a wide voltage range more negative than zero, but it increases markedly at positive voltages. The single channel currents measured over this same voltage range show that the single channel conductance is independent of voltage, but that channel gating properties are dependent on voltage. Both the mean channel open time and the opening rate increase at positive voltages. These properties change in a manner consistent with the voltage dependence of the macroscopic conductance. The broad range of similarities between the macroscopic and single channel currents supports the conclusion that the 40-pS channel that we have observed is the principal channel underlying the response to light in these photoreceptors.
利用膜片钳技术研究了鲎腹侧光感受器的光激活电导。观察到通道（40 pS），其开放概率因光而大大增加。在一些细胞中，通道激活的潜伏期与宏观反应的潜伏期几乎相同，而在其他细胞中，通道潜伏期则长得多。与宏观电导一样，通道活性因光适应而降低，但因细胞内注射钙螯合剂乙二醇双四乙酸（EGTA）而增强。后一观察结果表明，通道激活不是光诱导细胞内钙升高的继发结果。采用双微电极电压钳方法测量光激活宏观电导的电压依赖性。发现该电导在比零更负的宽电压范围内是恒定的，但在正电压下显著增加。在相同电压范围内测量的单通道电流表明，单通道电导与电压无关，但通道门控特性取决于电压。平均通道开放时间和开放速率在正电压下均增加。这些特性的变化方式与宏观电导的电压依赖性一致。宏观电流和单通道电流之间广泛的相似性支持了这样的结论，即我们观察到的40-pS通道是这些光感受器对光反应的主要通道。
