Inhibitions of chloride transport and gap junction reduce fluid flow across the whole porcine ciliary epithelium.

PURPOSE: To study the effects of chloride transport and gap junction inhibitors on fluid formation across the porcine ciliary epithelium.

METHODS: A complete annulus of porcine iris-ciliary body preparation was mounted onto a modified Ussing type chamber to measure the fluid flow (FF) rate. The potential difference (PD) across the preparation was monitored simultaneously. The effects of several inhibitors on chloride transport and gap junction were studied. These included 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), 5-(N,N-dimethyl)amiloride hydrochloride (DMA), bumetanide, niflumic acid, and heptanol.

RESULTS: The average baseline FF rate was 2.56 +/- 0.07 microL/h per preparation (n = 33). DIDS (0.1 mM) or DMA (0.1 mM) showed no effect on both FF and PD when added to the blood side of the preparation. Bumetanide (0.1 mM), on the blood side, inhibited the FF by 46% and caused a slight depolarization of PD. Heptanol (3.5 mM) depolarized the PD and reduced FF by 45% and 78% through the blood and aqueous sides, respectively. Niflumic acid (1 mM at the aqueous side) also depolarized the PD and significantly inhibited the FF (62%).

CONCLUSIONS: The effects of the chloride transport inhibitors on fluid formation across the porcine iris-ciliary body were comparable to that in previous chloride transport studies. The results indicated that fluid secretion by the isolated porcine ciliary epithelium is mainly driven by chloride transport. However, there may be other unidentified ion movements that drive residual FF after chloride transport is inhibited.