A Role for GCAP2 in Regulating the Photoresponse GUANYLYL CYCLASE ACTIVATION AND ROD ELECTROPHYSIOLOGY IN GUCA1B KNOCK-OUT MICE
A Role for GCAP2 in Regulating the Photoresponse GUANYLYL CYCLASE ACTIVATION AND ROD ELECTROPHYSIOLOGY IN GUCA1B KNOCK-OUT MICE
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DOI：
10.1074/jbc.m804445200
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发表时间：
2008-10-24
影响因子：
4.8
通讯作者：
Dizhoor, Alexander M.
中科院分区：
文献类型：
--
作者：
Makino, Clint L.;Peshenko, Igor V.;Dizhoor, Alexander M.
环GMP作为视觉信号转导的第二信使，将视紫红质的光子吸收与离子通道的活性联系起来。光感受器中cGMP的合成由一对视网膜特异性鸟苷酸环化酶retGC 1和retGC-2支持。两个神经元钙传感器，GCAP 1和GCAP 2，赋予钙的敏感性鸟苷酸环化酶的活动，但每个GCAP的重要性和贡献是有争议的。为了探索这个问题，在小鼠中破坏了编码GCAP 2的基因GUCA 1B，并测试了敲除杆调节retGC和产生光反应的能力。敲除不损害杆活力或改变外段超微结构。retGC 1、retGC 2和GCAP-1表达水平没有发生代偿性变化，但GCAP 2的缺失以两种方式影响鸟苷酸环化酶活性：（a）低[Ca 2 +]时cGMP合成的最大速率下降2倍，（B）cGMP合成的半最大速率在高于正常[Ca 2 +]时达到。添加针对小鼠GCAP 2的抗体对野生型视网膜中的鸟苷酸环化酶活性产生类似的影响。GCAP 2敲除棒的闪光响应比正常情况下恢复得更慢。敲除杆变得更敏感的闪光灯和照明的步骤，但往往在较低的强度饱和，与野生型杆。因此，鸟苷酸环化酶活性的GCAP 2调节加快闪光和阶跃响应的恢复，并将视杆的操作范围调整为更高强度的环境照明。
Cyclic GMP serves as the second messenger in visual transduction, linking photon absorption by rhodopsin to the activity of ion channels. Synthesis of cGMP in photoreceptors is supported by a pair of retina-specific guanylyl cyclases, retGC1 and -2. Two neuronal calcium sensors, GCAP1 and GCAP2, confer Ca2+ sensitivity to guanylyl cyclase activity, but the importance and the contribution of each GCAP is controversial. To explore this issue, the gene GUCA1B, coding for GCAP2, was disrupted in mice, and the capacity for knock-out rods to regulate retGC and generate photoresponses was tested. The knock-out did not compromise rod viability or alter outer segment ultrastructure. Levels of retGC1, retGC2, and GCAP-1 expression did not undergo compensatory changes, but the absence of GCAP2 affected guanylyl cyclase activity in two ways; (a) the maximal rate of cGMP synthesis at low [Ca2+] dropped 2-fold and (b) the half-maximal rate of cGMP synthesis was attained at a higher than normal [Ca2+]. The addition of an antibody raised against mouse GCAP2 produced similar effects on the guanylyl cyclase activity in wild type retinas. Flash responses of GCAP2 knockout rods recovered more slowly than normal. Knock-out rods became more sensitive to flashes and to steps of illumination but tended to saturate at lower intensities, as compared with wild type rods. Therefore, GCAP2 regulation of guanylyl cyclase activity quickens the recovery of flash and step responses and adjusts the operating range of rods to higher intensities of ambient illumination.