Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan 48505, USA.
Am J Physiol Cell Physiol. 2012 May 1;302(9):C1413-20. doi: 10.1152/ajpcell.00426.2011. Epub 2012 Feb 15.
Although oxidative stress is a hallmark of important vascular disorders such as diabetic retinopathy, it remains unclear why the retinal microvasculature is particularly vulnerable to this pathophysiological condition. We postulated that redox-sensitive ion channels may play a role. Using H(2)O(2) to cause oxidative stress in microvascular complexes freshly isolated from the adult rat retina, we assessed ionic currents, cell viability, intracellular oxidants, and cell calcium by using perforated-patch recordings, trypan blue dye exclusion, and fura-2 fluorescence, respectively. Supporting a role for the oxidant-sensitive ATP-sensitive K (K(ATP)) channels, we found that these channels are activated during exposure of retinal microvessels to H(2)O(2). Furthermore, their inhibition by glibenclamide significantly lessened H(2)O(2)-induced microvascular cell death. Additional experiments established that by increasing the influx of calcium into microvascular cells, the K(ATP) channel-mediated hyperpolarization boosted the vulnerability of these cells to oxidative stress. In addition to the K(ATP) channel-dependent mechanism for increasing the lethality of oxidative stress, we also found that the vulnerability of cells in the capillaries, but not in the arterioles, was further boosted by a K(ATP) channel-independent mechanism, which our experiments indicated involves the oxidant-induced activation of calcium-permeable nonspecific cation channels. Taken together, our findings support a working model in which both K(ATP) channel-independent and K(ATP) channel-dependent mechanisms render the capillaries of the retina particularly vulnerable to oxidative stress. Identification of these previously unappreciated mechanisms for boosting the lethality of oxidants may provide new targets for pharmacologically limiting damage to the retinal microvasculature during periods of oxidative stress.
尽管氧化应激是糖尿病性视网膜病变等重要血管疾病的标志，但仍不清楚为什么视网膜微血管特别容易受到这种病理生理状态的影响。我们假设氧化还原敏感的离子通道可能起作用。我们使用 H2O2 使从成年大鼠视网膜中新鲜分离的微血管复合物产生氧化应激，分别使用穿孔贴片记录、锥虫蓝染料排斥和 fura-2 荧光来评估离子电流、细胞活力、细胞内氧化剂和细胞内钙。支持氧化剂敏感的 ATP 敏感的 K（KATP）通道发挥作用，我们发现这些通道在视网膜微血管暴露于 H2O2 时被激活。此外，用格列本脲抑制它们显著减轻了 H2O2 诱导的微血管细胞死亡。进一步的实验确定，通过增加钙流入微血管细胞，KATP 通道介导的超极化增加了这些细胞对氧化应激的易感性。除了 KATP 通道依赖性机制增加氧化应激的致死性外，我们还发现，毛细血管中的细胞（而非小动脉中的细胞）的易感性进一步被一种 KATP 通道非依赖性机制增强，我们的实验表明这种机制涉及氧化诱导的钙通透性非特异性阳离子通道的激活。总之，我们的研究结果支持这样一个工作模型，即 KATP 通道非依赖性和 KATP 通道依赖性机制使视网膜毛细血管特别容易受到氧化应激的影响。鉴定这些以前未被认识到的增强氧化剂致死性的机制可能为在氧化应激期间限制视网膜微血管损伤的药理学提供新的靶点。
