A QUANTITATIVE ACCOUNT OF THE ACTIVATION STEPS INVOLVED IN PHOTOTRANSDUCTION IN AMPHIBIAN PHOTORECEPTORS
A QUANTITATIVE ACCOUNT OF THE ACTIVATION STEPS INVOLVED IN PHOTOTRANSDUCTION IN AMPHIBIAN PHOTORECEPTORS
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DOI：
10.1113/jphysiol.1992.sp019111
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发表时间：
1992-04-01
影响因子：
5.5
通讯作者：
PUGH, EN
中科院分区：
文献类型：
--
作者：
LAMB, TD;PUGH, EN
1. 我们已经进行了理论分析的步骤，有助于在脊椎动物光感受器的光转导级联。 我们明确地只考虑了活化步骤，即我们没有处理失活反应。 从理论分析中我们得出结论，一个单一的光异构化导致磷酸二酯酶（PDE）的激活具有一个近似延迟斜坡的时间过程;延迟是由几个短的一阶延迟阶段贡献的. 我们推导出一种方法，用于提取PDE激活的时间过程中测得的电响应，我们应用这种方法记录的光响应从蝾螈棒。 结果证实了PDE激活的时间过程是一个延迟斜坡的预测，斜率与光强成正比，初始延迟约为10-20 ms. 我们推导出光感受器对光的电响应的近似解析解，包括明亮的闪光（各向同性条件）和单光子（涉及外段中环GMP的纵向扩散）。 对短暂闪光的响应被预测为遵循时间的延迟高斯函数，即在初始短延迟之后，响应应当开始与t2成比例地上升。 此外，响应强度关系被预测服从指数饱和。 这些预测与实验进行了比较，它表明，上升阶段的闪光响应准确地描述了一个非常宽的强度范围。 我们的结论是，该模型提供了一个全面的描述在分子水平上的光转导的激活步骤。
1. We have undertaken a theoretical analysis of the steps contributing to the phototransduction cascade in vertebrate photoreceptors. We have explicitly considered only the activation steps, i.e. we have not dealt with the inactivation reactions.2. From the theoretical analysis we conclude that a single photoisomerization leads to activation of the phosphodiesterase (PDE) with a time course which approximates a delayed ramp; the delay is contributed by several short first-order delay stages.3. We derive a method for extracting the time course of PDE activation from the measured electrical response, and we apply this method to recordings of the photoresponse from salamander rods. The results confirm the prediction that the time course of PDE activation is a delayed ramp, with slope proportional to light intensity; the initial delay is about 10-20 ms.4. We derive approximate analytical solutions for the electrical response of the photoreceptor to light, both for bright flashes (isotropic conditions) and for single photons (involving longitudinal diffusion of cyclic GMP in the outer segment). The response to a brief flash is predicted to follow a delayed Gaussian function of time, i.e. after an initial short delay the response should begin rising in proportion to t2. Further, the response-intensity relation is predicted to obey an exponential saturation.5. These predictions are compared with experiment, and it is shown that the rising phase of the flash response is accurately described over a very wide range of intensities. We conclude that the model provides a comprehensive description of the activation steps of phototransduction at a molecular level.