CONTROL OF CA-2+ IN ROD OUTER SEGMENT DISKS BY LIGHT AND CYCLIC-GMP
CONTROL OF CA-2+ IN ROD OUTER SEGMENT DISKS BY LIGHT AND CYCLIC-GMP
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DOI：
10.1038/303344a0
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发表时间：
1983-01-01
期刊：
影响因子：
64.8
通讯作者：
HAGINS, WA
中科院分区：
文献类型：
--
作者：
GEORGE, JS;HAGINS, WA
脊椎动物视杆细胞吸收的光子可能通过改变可扩散的递质物质的细胞质浓度，减少黑暗中流入细胞外段的Na+电流，产生观察到的膜超极化，这是最初的兴奋反应1-4，从而引起感光细胞膜的电化学变化。由于在视杆细胞盘膜中发现了光激活的环GMP磷酸二酯酶(PDE)，并且细胞内注射环状GMP7降低了视杆细胞膜的电位，因此环GMP被认为是感光细胞质膜的递质。游离钙也被提出，因为快速和可逆地增加外部[钙]会降低暗电流，而二价阳离子团会增加钙的敏感性。完整视网膜视杆外段(ROS)的Ca~(2+)外流与光反应同时发生。由ROS盘膜制备的囊泡在光照下变得更具通透性，释放捕获的离子或分子11-13，但以前没有发现完整的外段盘能在黑暗中储存足够的Ca~(2+)和在光中释放足够的Ca~(2+)，以满足通过改变细胞质Ca~(2+)来控制暗电流的理论要求(参考文献14-18)。我们现在报告的实验表明，悬浮在含有高能磷酸酯和电解质的介质中的杆状盘膜需要储存和释放钙离子，这些物质与活的杆状细胞的细胞质组成相似。环状GMP可刺激ROS膜上钙离子的摄取。
Photons absorbed in vertebrate rods and cones probably cause electrochemical changes at the photoreceptor plasma membrane by changing the cytoplasmic concentration of a diffusible transmitter substance, reducing the Na+current flowing into the outer segment of the cell in the dark, to produce the observed membrane hyperpolarization that is the initial excitatory response1–4. Cyclic GMP has been proposed as the transmitter because a light-activated cyclic GMP phosphodiesterase (PDE) has been found in rod disk membranes5,6and because intracellularly injected cyclic GMP7reduces rod membrane potentials. Free Ca2+has also been proposed because increasing external [Ca2+] quickly and reversibly reduces the dark current and divalent cationophores increase the Ca2+sensitivity8. Ca2+efflux from rod outer segments (ROS) of intact retinas occurs simultaneously with light responses9,10. Vesicles prepared from ROS disk membranes become more permeable on illumination, releasing trapped ions or molecules11–13, but intact outer segment disks have not previously been found to store sufficient Ca2+in darkness and to release enough in light to meet the theoretical requirements for control of the dark current by varying cytoplasmic Ca2+(refs 14–18). We now report experiments that show the required Ca2+storage and release from rod disk membranes suspended in media containing high-energy phosphate esters and electrolytes approximating the cytoplasmic composition of live rod cells. Cyclic GMP stimulates Ca2+uptake by ROS disks in such media.