Gotow T, Nishi T, Kijima H
Department of Physiology, School of Medicine, Kagoshima University, Japan.
Neurosci Res Suppl. 1990;12:S145-59. doi: 10.1016/0921-8696(90)90016-v.
A photoreceptor potential produced by a decrease in membrane conductance was not thought to occur in any invertebrate photoreceptors. However, we have found that the molluscan extraocular photoreceptor, A-P-1 responds to light with a depolarizing receptor potential due to a decrease in K+ conductance, so that the photoresponse associated with a decrease in membrane conductance is not unique to the vertebrate photoreceptor. The properties that the light-suppressible K+ conductance is time- and voltage-dependent are explained by comparison with those of the single channel conductance obtained in patch-clamp of both vertebrate and invertebrate photoreceptors. The noise analysis of the light-induced current suggest that this macroscopic light-suppressible conductance consists of channels. It is concluded that the light-suppressible K+ conductance is mediated by hydrolysis of cGMP which reduces internal cGMP, in agreement with the cGMP hypothesis of vertebrate phototransduction and that the hydrolysis may be modified by IP3.
膜电导降低所产生的光感受器电位被认为不会出现在任何无脊椎动物的光感受器中。然而，我们发现软体动物的眼外光感受器A-P-1对光的反应是由于K⁺电导降低而产生去极化的感受器电位，因此与膜电导降低相关的光反应并非脊椎动物光感受器所特有。通过与脊椎动物和无脊椎动物光感受器膜片钳实验中获得的单通道电导特性进行比较，解释了光可抑制的K⁺电导具有时间和电压依赖性的特性。对光诱导电流的噪声分析表明，这种宏观的光可抑制电导由通道组成。得出的结论是，光可抑制的K⁺电导是由cGMP水解介导的，cGMP水解会降低细胞内cGMP，这与脊椎动物光转导的cGMP假说一致，并且这种水解可能会被IP₃修饰。
