ROLE OF CYCLIC GMP IN ROD PHOTORECEPTOR FUNCTION

本研究的目的是阐明生化机制， cGMP影响脊椎动物视杆细胞的视觉传导 光感受器 cGMP途径的生物化学研究（视紫红质） GTP结合蛋白磷酸二酯酶）和电生理效应 cGMP在全细胞记录和分离的膜斑上的浓度表明， cGMP在调节光依赖性通透性中的重要性 在细胞膜上的机制。 cGMP的分子机制 然而，行为尚未确定。 拟议研究的目的如下： (1)评价光诱导的总cGMP的小幅降低是否 浓度反映了cGMP浓度的较大变化， 细胞质 观察到的总cGMP浓度下降太小 通过一个简单的方法对渗透机制产生显著的影响， 绑定模型 然而，cGMP的亚细胞分配到游离和 可能出现结合池，并将通过分离总细胞 cGMP，以确定总cGMP的显著部分是否被结合， 因此对磷酸二酯酶快速光诱导水解不敏感。 (2)确定cGMP在视杆中的可能作用部位。 cGMP已知 影响质膜离子渗透性、Ca 2+释放 从盘膜，蛋白激酶活性，和GTP结合蛋白。 cGMP结合位点的鉴定和表征将导致 纯化可能通过cGMP变化进行调节的蛋白质组分 浓度和/或结合，棒的离子渗透性。 这些实验应该允许对各种模型进行更明确的测试， cGMP在视觉传导中的作用，并导致对 为什么cGMP代谢缺陷会导致感光细胞变性， 死亡

The objective of this research is to elucidate the biochemical mechanism by which cGMP influences visual transduction in vertebrate rod photoreceptors. Both biochemical studies of the cGMP pathway (rhodopsin to GTP-bining protein to phosphodiesterase) and electrophysiological effects of cGMP on whole cell recordings and isolated membrane patches demonstrate the importance of cGMP in modulating the light-dependent permeability mechanism in the plasma membrane. The molecular mechanism by which cGMP acts has not, however, been determined. The aims of the proposed research are as follows: (1) To evaluate whether small light-induced decreases in total cGMP concentration reflect larger changes in cGMP concentration in the cytoplasm. The observed decrease in total cGMP concentration is too small to exert a significant effect on the permeability mechanism by a simple binding model. However, subcellular partitioning of cGMP into free and bound pools may occur, and will be examined by fractionating total cellular cGMP to determine whether a significant portion of total cGMP is bound and hence not sensitive to rapid light-induced hydrolysis by phosphodiesterse. (2) To identify possible sites of action of cGMP in the rod. cGMP is known to have effects on ion permeability of the plasma membrane, Ca2+ release from disc membranes, protein kinase activity, and GTP-binding protein. Identification and characterization of cGMP binding sites will lead to purification of protein components that may regulate, via changes in cGMP concentration and/or binding, the ionic permeability of the rod. These experiments should permit more definitive tests of various models for cGMP action in visual transduction, and lead to increased understanding of why defects in cGMP meatabolism lead to photoreceptor cell degeneration and death.