PHOTORECEPTOR CHANNEL ACTIVATION - INTERACTION BETWEEN CAMP AND CGMP
PHOTORECEPTOR CHANNEL ACTIVATION - INTERACTION BETWEEN CAMP AND CGMP
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DOI：
10.1021/bi00433a007
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发表时间：
1989-04-04
期刊：
影响因子：
2.9
通讯作者：
TANAKA, JC
中科院分区：
文献类型：
--
作者：
FURMAN, RE;TANAKA, JC
CAMP激活从杆状外段切除的斑块中的电流。在cAMP饱和浓度下的电流是.apprx。25%的电流被光转导中的终末胞质信使cGMP激活。CAMP的K0.5为1.5 mm，协作性指数为.apprx。1.4.CAMP激活的通道数与cGMP激活的通道数相同，因为在两个核苷酸存在的情况下，电流小于单个反应的总和。当增加的cAMP浓度(小于其K0.5)加入到固定的亚饱和浓度的cGMP中时，cAMP的总电流比单独cGMP产生的电流显著增加。这些结果是通过三位点、线性、顺序结合方案预测的，其中cAMP或cGMP可以与通道上的相同位点结合。在.apprx。5微米cGMP，估计是脊椎动物光感受器的稳定暗水平，cAMP在1到100微米之间会使光感受器电流大幅增加。讨论了cAMP-cGMP相互作用在光信号转导中可能的生理作用。
cAMP activates a current in excised patches from rod outer segments. The current at saturating concentrations of cAMP is .apprx. 25% of the current activated with 200 .mu.M cGMP, the terminal cytoplasmic messenger in phototransduction. The K0.5 for cAMP is > 1.5 mM, and the index of cooperativity is .apprx. 1.4. cAMP activates the same population of channels as activated by cGMP since currents in the presence of both nucleotides are less than the sum of the individual responses. When increasing concentrations of cAMP, less than its K0.5, are added to a fixed, subsaturating concentration of cGMP, cAMP significantly enhances the total current compared with the current produced by cGMP alone. These results are predicted by a three-site, linear, sequential binding scheme where either cAMP or cGMP may bind to the same site on the channel. At .apprx. 5 .mu.M cGMP, which is estimated to be the steady-state dark level in vertebrate photoreceptors, cAMP between 1 and 100 .mu.M produces a large increase in the photoreceptor current. A possible physiological role for cAMP-cGMP interaction in phototransduction is discussed.