Mitchell C H, Carré D A, McGlinn A M, Stone R A, Civan M M
Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6085, USA.
Proc Natl Acad Sci U S A. 1998 Jun 9;95(12):7174-8. doi: 10.1073/pnas.95.12.7174.
Purines can modify ciliary epithelial secretion of aqueous humor into the eye. The source of the purinergic agonists acting in the ciliary epithelium, as in many epithelial tissues, is unknown. We found that the fluorescent ATP marker quinacrine stained rabbit and bovine ciliary epithelia but not the nerve fibers in the ciliary bodies. Cultured bovine pigmented and nonpigmented ciliary epithelial cells also stained intensely when incubated with quinacrine. Hypotonic stimulation of cultured epithelial cells increased the extracellular ATP concentration by 3-fold; this measurement underestimates actual release as the cells also displayed ecto-ATPase activity. The hypotonically triggered increase in ATP was inhibited by the Cl--channel blocker 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) in both cell types. In contrast, the P-glycoprotein inhibitors tamoxifen and verapamil and the cystic fibrosis transmembrane conductance regulator (CFTR) blockers glybenclamide and diphenylamine-2-carboxylate did not affect ATP release from either cell type. This pharmacological profile suggests that ATP release is not restricted to P-glycoprotein or the cystic fibrosis transmembrane conductance regulator, but can proceed through a route sensitive to NPPB. ATP release also was triggered by ionomycin through a different NPPB-insensitive mechanism, inhibitable by the calcium/calmodulin-activated kinase II inhibitor KN-62. Thus, both layers of the ciliary epithelium store and release ATP, and purines likely modulate aqueous humor flow by paracrine and/or autocrine mechanisms within the two cell layers of this epithelium.
嘌呤可调节睫状体上皮向眼内房水的分泌。与许多上皮组织一样，作用于睫状体上皮的嘌呤能激动剂的来源尚不清楚。我们发现，荧光ATP标记物喹吖因可使兔和牛的睫状体上皮染色，但不能使睫状体中的神经纤维染色。用喹吖因孵育时，培养的牛色素性和非色素性睫状体上皮细胞也强烈染色。低渗刺激培养的上皮细胞可使细胞外ATP浓度增加3倍；由于细胞还表现出胞外ATP酶活性，因此该测量值低估了实际释放量。在两种细胞类型中，Cl-通道阻滞剂5-硝基-2-(3-苯丙基氨基)苯甲酸(NPPB)均抑制了低渗触发的ATP增加。相比之下，P-糖蛋白抑制剂他莫昔芬和维拉帕米以及囊性纤维化跨膜传导调节因子(CFTR)阻滞剂格列本脲和二苯胺-2-羧酸盐对两种细胞类型的ATP释放均无影响。这种药理学特征表明，ATP释放并不局限于P-糖蛋白或囊性纤维化跨膜传导调节因子，而是可以通过对NPPB敏感的途径进行。离子霉素也通过一种不同的对NPPB不敏感的机制触发ATP释放，该机制可被钙/钙调蛋白激活的激酶II抑制剂KN-62抑制。因此，睫状体上皮的两层均储存和释放ATP，嘌呤可能通过该上皮的两个细胞层内的旁分泌和/或自分泌机制调节房水流动。
