Candia O A, Shi X P, Chu T C
Department of Ophthalmology, Mount Sinai School of Medicine, New York, NY 10029.
Curr Eye Res. 1991 Mar;10(3):197-203. doi: 10.3109/02713689109003441.
In a physiological medium (134 mM Na+ concentration), unidirectional blood-to-aqueous and aqueous-to-blood Na+ fluxes across the isolated rabbit ciliary epithelium are large, rendering the detection of a net transport difficult. At 134 mM an active component for Na+ may be obscured by diffusional fluxes and a bidirectional Na(+)-Cl- cotransport. Considering that the active transport saturates at about 30 mM, experiments were performed at this reduced Na+ concentration to minimize the influence of diffusional pathways. A net blood-to-aqueous Na+ flux that ranged from 0.25 to 0.81 mu eq/hr was obtained. Addition of ascorbic acid to the aqueous side under this condition increased the blood-to-aqueous flux with little effect on the flux in the opposite direction. Ouabain inhibited both the Na+ and ascorbate-stimulated Na+ transport. The increase in blood-to-aqueous Na+ flux by ascorbate was also observed in tissues bathed with [Na+] closer to physiological levels (100 mM). These results indicate that the rabbit ciliary epithelium transports Na+ into the posterior chamber. Since aqueous ascorbate stimulates Na+ transport, it may be implicated in both Na+ movement and aqueous humor secretion. However, the rate of Na+ transport can only account for a small fraction of total aqueous humor production.
在生理介质（钠离子浓度为134 mM）中，分离的兔睫状上皮细胞中钠离子从血液到房水以及从房水到血液的单向通量很大，使得检测净转运变得困难。在134 mM时，钠离子的主动转运成分可能会被扩散通量和双向钠氯共转运所掩盖。考虑到主动转运在约30 mM时达到饱和，因此在降低的钠离子浓度下进行实验，以尽量减少扩散途径的影响。获得了范围在0.25至0.81微当量/小时的从血液到房水的钠离子净通量。在此条件下，向房水侧添加抗坏血酸会增加从血液到房水的通量，而对相反方向的通量影响很小。哇巴因抑制了钠离子和抗坏血酸刺激的钠离子转运。在用更接近生理水平（100 mM）的[钠离子]浸泡的组织中，也观察到抗坏血酸使从血液到房水的钠离子通量增加。这些结果表明，兔睫状上皮细胞将钠离子转运到后房。由于房水中的抗坏血酸刺激钠离子转运，它可能与钠离子移动和房水分泌都有关。然而，钠离子转运速率仅占房水总生成量的一小部分。
