Chloride and sodium transport across bovine ciliary body/epithelium (CBE)

Purpose. To study the chloride and sodium ion transports across the bovine ciliary body/epithelium (CBE) by a modified Ussing-Zerahn type chamber. Methods. Isolated bovine CBE preparations were mounted in a modified Ussing-type chamber and the transepithelial electrical parameters were monitored. The inward (stroma to aqueous) and outward (aqueous to stroma) fluxes of36[Cl] chloride and22[Na] sodium ions across the CBE were measured under short-circuited conditions. The effect of 0.1 mM of furosemide and bumetanide on the chloride transport were studied. Results. The potential difference (PD), the resistance and the short-circuit current (SCC) across the isolated bovine ciliary body were found to be -0.20 ± 0.01 mV (aqueous negative), 75 ± 1 Ωcm2and -2.70 ± 0.17 μAcm-2(mean ± SEM, n = 50) respectively. A statistically significant net inward chloride ion flux of 1.12 ± 0.41 μEq h-1cm-2(p < 0.01) was found (n = 15). The net chloride transport was abolished when 0.1 mM furosemide (82% inhibition) and 0.1 mM bumetanide (100% inhibition) were applied bilateral. No significant net sodium ion flux was detected. Conclusions. Electrolyte and fluid transport across the bovine CBE may be via a bumetanide and furosemide-sensitive chloride transport mechanism. The Na-K-2Cl cotransporter plays a significant role in the trans-CBE chloride transport. The net chloride flux/current was about 12 times higher than the measured SCC, suggesting that the chloride ion transport may be coupled to other ion species.