Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan 48505, USA.
Invest Ophthalmol Vis Sci. 2011 Dec 9;52(13):9345-52. doi: 10.1167/iovs.11-8176.
It is uncertain why retinal capillaries are particularly vulnerable to hypoxia. In this study, it was hypothesized that their specialized physiology, which includes being the predominant microvascular location of functional adenosine triphosphate-sensitive potassium (K(ATP)) channels, boosts their susceptibility to hypoxia-induced cell death.
Cell viability, ionic currents, intracellular calcium, and pericyte contractility in microvascular complexes freshly isolated from the rat retina were assessed using trypan blue dye exclusion, perforated-patch recordings, fura-2 fluorescence, and time-lapse videos. Chemical hypoxia was induced by antimycin, an oxidative phosphorylation inhibitor.
In freshly isolated retinal microvascular complexes, chemical hypoxia caused more cell death in capillaries than in arterioles. Indicative of the role of polyamine-dependent K(ATP) channels, antimycin-induced capillary cell death was markedly decreased in microvessels treated with the polyamine synthesis inhibitor, difluoromethylornithine, or the K(ATP) channel inhibitor, glibenclamide. These inhibitors also diminished the antimycin-induced hyperpolarization, as well as the antimycin-induced intracellular calcium increase, which was significantly dependent on extracellular calcium and was diminished by the inhibitor of calcium-induced calcium release (CICR), dantrolene. Consistent with the importance of the CICR-dependent increase in capillary cell calcium, dantrolene significantly decreased hypoxia-induced capillary cell death. We also found that activation of the polyamine/K(ATP) channel/Ca(2+) influx/CICR pathway not only boosted the vulnerability of retinal capillaries to hypoxia, but also caused the contraction of capillary pericytes, whose vasoconstrictive effect may exacerbate hypoxia.
The vulnerability of retinal capillaries to hypoxia is boosted by a mechanism involving the polyamine/K(ATP) channel/Ca(2+) influx/CICR pathway. Discovery of this pathway should provide new targets for pharmacological interventions to minimize hypoxia-induced damage in retinal capillaries.
尚不清楚为何视网膜毛细血管特别容易受到缺氧的影响。在本研究中，我们假设其特化的生理学特性（包括成为功能性三磷酸腺苷敏感性钾通道（K(ATP)）的主要微血管位置）会增加其对缺氧诱导的细胞死亡的敏感性。
采用台盼蓝染料排斥、穿孔膜片钳记录、钙荧光染料 fura-2 荧光和延时视频，评估从大鼠视网膜中新鲜分离的微血管复合物中的细胞活力、离子电流、细胞内钙和周细胞收缩性。通过抗霉素诱导化学缺氧，抗霉素是一种氧化磷酸化抑制剂。
在新鲜分离的视网膜微血管复合物中，化学缺氧引起的毛细血管细胞死亡比小动脉多。抗霉素诱导的毛细血管细胞死亡明显减少，这表明多胺依赖性 K(ATP)通道的作用，在用多胺合成抑制剂二氟甲基鸟氨酸或 K(ATP)通道抑制剂格列本脲处理的微血管中。这些抑制剂还减弱了抗霉素诱导的超极化，以及抗霉素诱导的细胞内钙增加，这主要依赖于细胞外钙，并且被钙诱导钙释放（CICR）抑制剂丹曲林钠减弱。与 CICR 依赖性增加毛细血管细胞钙的重要性一致，丹曲林钠显著降低了缺氧诱导的毛细血管细胞死亡。我们还发现，多胺/K(ATP)通道/钙内流/CICR 通路的激活不仅增加了视网膜毛细血管对缺氧的敏感性，还导致了毛细血管周细胞的收缩，其血管收缩作用可能会加剧缺氧。
涉及多胺/K(ATP)通道/钙内流/CICR 通路的机制增强了视网膜毛细血管对缺氧的敏感性。发现该通路应提供新的药物干预靶点，以最小化视网膜毛细血管缺氧引起的损伤。
