α2 adrenergic receptor-mediated modulation of cytosolic Ca++ signals at the inner plexiform layer of the rat retina
α2 adrenergic receptor-mediated modulation of cytosolic Ca++ signals at the inner plexiform layer of the rat retina
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DOI：
10.1167/iovs.06-0890
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发表时间：
2007-03-01
影响因子：
4.4
通讯作者：
Hare, William A.
中科院分区：
文献类型：
--
作者：
Dong, Cun-Jian;Guo, Yuanxing;Hare, William A.
目的。令人信服的证据表明，在广泛的动物模型中，α - 2激动剂，如苯丙胺，可以保护视网膜神经节细胞（RGCs）免受损伤。然而，这种保护的作用机制和α 2肾上腺素能系统在视网膜中的生理作用尚不清楚。这项工作的一个主要目标是探索α 2肾上腺素能系统在视网膜突触层，特别是内丛状层（IPL）的胞质Ca2+信号的调节中的作用，其中rgc与其突触前细胞之间的通信发生。采用高速共聚焦系统对活体大鼠视网膜内丛状层（IPL）和外丛状层（OPL）进行功能Ca2+成像。用荧光Ca2+染料fluo-4监测胞质游离Ca2+的相对变化。Ca2+信号是由高K+ (40 mM)林格溶液产生的膜去极化引起的，该溶液通过定制的多通道局部灌注系统快速而短暂地输送到视网膜切片的测试区域。在IPL和OPL下，短暂的高K+林格处理（8秒）引起细胞质内Ca2+的增加。在这两种情况下，这种Ca2+信号被尼莫地平（一种选择性的l型电压门控Ca2+通道阻滞剂）或用等量的EGTA取代林格格中的细胞外Ca2+时消除。在IPL， Ca2+信号也被溴胺定和其他α 2受体激动剂（如美托咪定）以剂量依赖性的方式抑制。经典α - 2受体拮抗剂如育亨宾、劳沃尔辛和阿替帕唑完全阻断溴莫尼定和美托咪定的抑制作用。有趣的是，α 2受体激动剂对高K+林格诱导的OPL细胞质Ca2+信号没有影响。用D-AP5阻断n -甲基-i)-天冬氨酸（NMDA）型的异离子型谷氨酸受体，可在IPL下将这种高K+诱导的Ca2+信号减弱约20%。D-AP5对opl的Ca2+信号没有影响。这些发现为中枢神经系统（视网膜是中枢神经系统的一部分）中α 2受体介导的l型Ca2+通道活性的调节提供了第一个直接证据。这种α - 2调制似乎发生在视网膜的外视层，而不是外视层。这些发现表明，视网膜α - 2系统的生理功能是调节IPL的突触传递，并且苯丙胺和其他α - 2激动剂可能通过防止RGCs及其突触前细胞或两者的胞质游离Ca2+异常升高来保护疾病条件下的RGCs。
PURPOSE. Compelling evidence suggests that alpha 2 agonists, such as brimonidine, protect retinal ganglion cells (RGCs) from injury in a wide range of animal models. However, the mechanism of action for this protection and the physiological role of the alpha 2 adrenergic system in the retina is not well understood. A major goal of this work was to explore the role of the alpha 2 adrenergic system in the modulation of cytosolic Ca2+ signaling at retinal synaptic layers, particularly the inner plexiform layer (IPL), where communication between RGCs and their presynaptic cells takes place.METHODS. Functional Ca2+ imaging at the inner plexiform layer (IPL) and outer plexiform layer (OPL) of living rat retinal slices was conducted with a high-speed confocal system. The relative changes of cytosolic free Ca2+ were monitored with the fluorescent Ca2+ dye fluo-4. The Ca2+ signal was elicited by membrane depolarization produced by a high K+ (40 mM) Ringer solution that was delivered rapidly and briefly to the test regions of the retinal slice by a custom-made multichannel local perfusion system.RESULTS. A brief application (8 seconds) of high K+ Ringer elicited a robust cytosolic Ca2+ increase at the IPL and OPL. In both cases, this Ca2+ signal was eliminated by nimodipine, a selective L-type voltage-gated Ca2+-channel blocker, or when the extracellular Ca2+ in the Ringer was replaced with equal molar EGTA. At IPL, the Ca2+ signal was also suppressed in a dose-dependent manner by brimonidine and other alpha 2 receptor agonists, such as medetomidine. The suppressive action of brimonidine and medetomidine was completely blocked by classic alpha 2 receptor antagonists, such as yohimbine, rauwolscine, and atipamezole. Interestingly, the alpha 2 receptor agonists had no effect on the high K+ Ringer-elicited cytosolic Ca2+ signal at OPL. Blocking the N-methyl-i)-aspartate (NMDA) type of ionotropic glutamate receptor with D-AP5 attenuated this high K+-elicited Ca2+ signal by approximately 20% at IPL. D-AP5 had no effect on the Ca2+ signal at OPL.CONCLUSIONS. These findings provide the first direct evidence of alpha 2 receptor-mediated modulation of L-rype Ca2+ channel activity in the CNS (the retina is part of the CNS). This alpha 2 modulation appears to occur at the IPL but not at the OPL of the retina. These findings suggest that a physiological function of the retinal alpha 2 system is the regulation of synaptic transmission at IPL and that brimonidine and other alpha 2 agonists may protect RGCs under disease conditions by preventing abnormal elevation of cytosolic free Ca2+ either in RGCs, in their presynaptic cells, or in both.