Chloride and bicarbonate ion transport across isolated bovine Iris-Ciliary Body (ICB)

Purpose : To study the chloride and bicarbonate ions transport of bovine ICB by a modified Ussing-Zerahn type chamber and to study active transport of ions which may be implicated in the aqueous humour production of the eye. Methods: Bovine ICB preparations were mounted in a Ussing type chamber (area=0.35cm2) and the transepithelial electrical parameters were monitored. The inward (from the stromal to the aqueous side) and the outward (from the aqueous to the stromal side) fluxes of [36Cl] chloride and [14C]bicarbonate ions across the isolated bovine iris-ciliary body were measured using the modified Ussing-Zerahn type chamber under short-circuited condition. Results: The p.d. across the bovine ICB was 0.19±0.01mV (aqueous negative) and the short circuited current (SCC) was 1.89±0.12μA cm-2, (mean±SEM, n=46). The inward and outward bicarbonate ions fluxes were 1.04±0.05 and 1.03±0.06μeq hr-1cm-2(Mean ± SEM, n=11) respectively. The inward and outward chloride ions fluxes were 4.50±0.22 and 3.69±0.21μeq hr-1cm-2(Mean ± SEM, n=12) respectively. No significant net bicarbonate ion flux was detected in either directions. However, a statistically significant inward chloride flux of 0.81±0.3μeq hr-1cm-2(p=0.01) was detected. Conclusions: No net flux of bicarbonate ion was found in either directions but a net chloride flux was evident in the direction from stromal to aqueous side. The net chloride flux or current is about 13 times higher than the measured SCC. It suggests that the chloride ion transport may be electrically coupled to other ion species. The results indicate that active chloride ion transport may take part in the secretion of aqueous humour.