Bonanno J A, Klyce S D, Cragoe E J
Lions Eye Research Laboratories, Louisiana State University Medical Center, School of Medicine, New Orleans 70112.
Am J Physiol. 1989 Aug;257(2 Pt 1):C290-6. doi: 10.1152/ajpcell.1989.257.2.C290.
The mechanism of chloride uptake at the basal membrane (stromal side) of rabbit corneal epithelium was examined by observing the effects of ion transport inhibitors and ion concentrations on the stimulated epithelial short-circuit current (Isc). Loop diuretics inhibited the theophylline-stimulated peak and sustained Isc. Treatment with 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS, 0.2 mM) and/or 5-(N,N-dimethyl)amiloride (0.1 mM) as well as the potent anion exchange inhibitor, 5c(+)[(2,3,9,9a-tetrahydro-1H-fluoren-7-yl)oxy]acetic acid (0.01 mM), had no significant effect on Isc. These results are consistent with Cl- uptake by a Na+-Cl- or Na+-K+-2Cl- cotransport mechanism rather than Cl(-)-HCO3(-)-OH- exchange coupled to Na+-H+ exchange. Incubation in low [Na+] or [Cl-] before stimulation with forskolin (0.1 mM) reduced both peak and sustained Isc, and saturation kinetics were exhibited. Hill coefficients for [Na+] and [Cl-] were 0.99 and 1.04, respectively, for peak Isc and 0.66 and 1.18, respectively, for sustained Isc. Apparent ion affinities for Na+ and Cl- were 13.5 and 18 mM, respectively, for peak Isc and 15 and 22 mM, respectively, for sustained Isc. These results favor Cl- uptake by a 1 Na+:1 Cl- cotransport mechanism for the rabbit corneal epithelium, but involvement of K+ in this process has not been eliminated.
通过观察离子转运抑制剂和离子浓度对刺激后的上皮短路电流（Isc）的影响，研究了兔角膜上皮基底膜（基质侧）氯离子摄取的机制。袢利尿剂抑制了茶碱刺激的峰值和持续的Isc。用4,4'-二异硫氰基芪-2,2'-二磺酸（DIDS，0.2 mM）和/或5-（N，N-二甲基）阿米洛利（0.1 mM）以及强效阴离子交换抑制剂5c(+)[(2,3,9,9a-四氢-1H-芴-7-基)氧基]乙酸（0.01 mM）处理对Isc没有显著影响。这些结果与通过Na+-Cl-或Na+-K+-2Cl-共转运机制摄取Cl-一致，而不是与Na+-H+交换偶联的Cl(-)-HCO3(-)-OH-交换。在用福司可林（0.1 mM）刺激前，在低[Na+]或[Cl-]中孵育会降低峰值和持续的Isc，并表现出饱和动力学。对于峰值Isc，[Na+]和[Cl-]的希尔系数分别为0.99和1.04，对于持续Isc分别为0.66和1.18。对于峰值Isc，Na+和Cl-的表观离子亲和力分别为13.5和18 mM，对于持续Isc分别为15和22 mM。这些结果支持兔角膜上皮通过1 Na+:1 Cl-共转运机制摄取Cl-，但尚未排除K+参与这一过程。
