Holcombe David J, Lengefeld Nadia, Gole Glen A, Barnett Nigel L
School of Biomedical Sciences, University of Queensland, Brisbane, Queensland, Australia.
Acta Ophthalmol. 2008 Jun;86(4):408-14. doi: 10.1111/j.1600-0420.2007.01052.x. Epub 2007 Nov 19.
To investigate the relationship between intraocular pressure (IOP), retinal glutamate transport and retinal hypoxia during acute IOP elevations of varying magnitude.
Female Dark Agouti rats were anaesthetized by ketamine/xylazine/acepromazine (10/5/0.5 mg/kg i.p.). The anterior chamber was cannulated with a 30-gauge needle attached to a saline reservoir. The target IOP (20-120 mmHg, in 10 mmHg increments) was obtained by adjusting the reservoir height. After 10 mins of IOP stabilization, 2 microl of the non-endogenous glutamate transporter substrate, D-aspartate, was injected into the vitreous (final concentration 50 microm), and the elevated IOP maintained for a further 60 mins (total duration of IOP elevation was 70 mins). Glutamate transporter function was assessed by the immunohistochemical localization of D-aspartate. Retinal sections were examined for histological integrity. The experiment was repeated substituting the D-aspartate with the cellular hypoxia marker, Hypoxyprobe-1.
Under control conditions, D-aspartate was preferentially taken up into the glial Müller cells by glutamate/aspartate transporter (GLAST). This function was maintained at pressures < or = 70 mmHg, whereafter perturbation of function was evidenced by decreased accumulation of D-aspartate by Müller cells. Failure of GLAST activity was coincident with the appearance of Hypoxyprobe-labelled cells in the inner retina and histological damage.
Glutamate transport does not appear to change linearly with increased IOP. A pressure threshold exists, above which Müller cell GLAST function is compromised. Moreover, ganglion cell glutamate uptake is only apparent at pressures above those that cause GLAST inhibition. The association between IOP, hypoxia, glutamate transporter dysfunction and subsequent retinal cell death may have important implications for the pathogenesis of IOP/ischaemia-related neuropathy and neuroprotective strategies.
研究不同程度急性眼压升高期间眼压（IOP）、视网膜谷氨酸转运和视网膜缺氧之间的关系。
雌性黑褐大鼠用氯胺酮/赛拉嗪/乙酰丙嗪（10/5/0.5毫克/千克腹腔注射）麻醉。用连接盐水储液器的30号针头插入前房。通过调整储液器高度获得目标眼压（20 - 120毫米汞柱，以10毫米汞柱递增）。眼压稳定10分钟后，将2微升非内源性谷氨酸转运体底物D - 天冬氨酸注入玻璃体（终浓度50微摩尔），并将升高的眼压维持60分钟（眼压升高总时长70分钟）。通过D - 天冬氨酸的免疫组织化学定位评估谷氨酸转运体功能。检查视网膜切片的组织学完整性。用细胞缺氧标记物Hypoxyprobe - 1替代D - 天冬氨酸重复该实验。
在对照条件下，D - 天冬氨酸通过谷氨酸/天冬氨酸转运体（GLAST）优先被摄取到神经胶质Müller细胞中。该功能在眼压≤70毫米汞柱时得以维持，此后Müller细胞对D - 天冬氨酸的摄取减少证明功能受到干扰。GLAST活性丧失与内视网膜中Hypoxyprobe标记细胞的出现及组织学损伤同时发生。
谷氨酸转运似乎不会随眼压升高呈线性变化。存在一个压力阈值，高于此阈值Müller细胞GLAST功能受损。此外，神经节细胞谷氨酸摄取仅在高于导致GLAST抑制的压力时才明显。眼压、缺氧、谷氨酸转运体功能障碍与随后视网膜细胞死亡之间的关联可能对眼压/缺血相关神经病变的发病机制及神经保护策略具有重要意义。
