McLaughlin C W, Peart D, Purves R D, Carré D A, Macknight A D, Civan M M
Department of Physiology, University of Otago Medical School, Dunedin, New Zealand.
Invest Ophthalmol Vis Sci. 1998 Aug;39(9):1631-41.
To determine whether the Na+-K+-2Cl- symport or the parallel Na+/H+ and Cl-/HCO3- antiports provide the dominant pathway for NaCl uptake into the ciliary epithelium. Both pathways are known to support NaCl entry from the stroma into the pigmented ciliary epithelial (PE) cells, after which Na+ and Cl- diffuse across the gap junctions into the nonpigmented ciliary epithelial (NPE) cells and are released into the aqueous humor.
Rabbit iris ciliary bodies were preincubated in HCO3-/CO2-containing or HCO3-/CO2-free solutions before quick freezing, cryosectioning, dehydration, and electron probe x-ray microanalysis.
The NPE and the PE cells contained more K and Cl when incubated with bicarbonate. Inhibition of carbonic anhydrase with 0.5 mM acetazolamide had little effect in HCO3--free medium but prevented the increase in Cl in both cell types in HCO3-/CO2 solution. Inhibition of the Na+-K+-2Cl- symport with 10 to 500 microM bumetanide caused Cl loss from both cell types in HCO3--free solution, but bumetanide produced a paradoxical increase in Cl and Na in HCO3-/CO2 solution. Together, acetazolamide and bumetanide resulted in significant Cl loss in HCO3--free solution and prevented the gains of Cl and Na in HCO3-/CO2 solution.
The present results indicate that the dominant entry pathway of NaCl from the stroma into the ciliary epithelial syncytium is through an acetazolamide-inhibitable Cl-/HCO3 and a parallel Na+/H+ antiport. The dominant release pathways into the aqueous humor appear to be a Na+-K+-2Cl-symport, which can be outwardly directed under physiological conditions, together with the Na+/K+-exchange pumps and Cl- channels.
确定钠-钾-2氯同向转运体或并行的钠/氢和氯/碳酸氢根反向转运体是否为氯化钠进入睫状体上皮的主要途径。已知这两种途径均支持氯化钠从基质进入色素性睫状体上皮（PE）细胞，之后钠和氯通过缝隙连接扩散到非色素性睫状体上皮（NPE）细胞，并释放到房水中。
兔虹膜睫状体在含或不含碳酸氢根/二氧化碳的溶液中预孵育，然后快速冷冻、冷冻切片、脱水并进行电子探针X射线微分析。
与碳酸氢盐一起孵育时，NPE和PE细胞含有更多的钾和氯。在无碳酸氢根的培养基中，用0.5 mM乙酰唑胺抑制碳酸酐酶几乎没有作用，但在碳酸氢根/二氧化碳溶液中可阻止两种细胞类型中氯的增加。用10至500 microM布美他尼抑制钠-钾-2氯同向转运体，在无碳酸氢根的溶液中导致两种细胞类型的氯流失，但在碳酸氢根/二氧化碳溶液中布美他尼使氯和钠出现反常增加。乙酰唑胺和布美他尼共同作用，在无碳酸氢根的溶液中导致显著的氯流失，并阻止了碳酸氢根/二氧化碳溶液中氯和钠的增加。
目前的结果表明，氯化钠从基质进入睫状体上皮合体的主要进入途径是通过乙酰唑胺可抑制的氯/碳酸氢根和并行的钠/氢反向转运体。进入房水的主要释放途径似乎是钠-钾-2氯同向转运体，在生理条件下它可以向外转运，还有钠/钾交换泵和氯通道。
