Non-selective anion pathway of bovine ciliary epithelium

Purpose: To investigate the roles of chloride ion and bicarbonate ion in transepithelial ionic transport of bovine ciliary epithelium. Methods: Sections of iris-ciliary body (I-CB) of bovine eye were mounted in Ussing-type chambers (area 0.35cm2) and prefused with normal Ringer solution at rate of 10mlhr-1. Transepithelial potential difference (p.d.) and short circuit current (SCC) of the preparations were measured. The effects of bicarbonate free Ringer solution in the presence or absence of carbonic anhydrase inhibitor (1mM acetazolamide) on I-CB preparations were studied. Changes in transepithelial electrical parameters were also observed when 30mM or 60mM of chloride ion were substituted by equal molar of either gluconate ion or bicarbonate ion. Results: The control p.d. measured was -0.45±0.04mV with the aqueous side consistently negative with respect to the blood side and the SCC was -4.62±0.63μA/cm2 (mean±SEM, n=25). There were no significant differences in the p.d. and SCC when the preparations were perfused with bicarbonate free Ringer (with or without acetazolamide) or normal Ringer solution. Significant changes in p.d. and SCC were found when either 30mM (-0.20±0.04mV, -1.86±0.48μA/cm2, n=16) or 60mM (-0.10±0.07mV, -0.94±0.72μA/cm2, n=9 respectively) of chloride ion was replaced by gluconate ion. No significant changes were observed when chloride ion was substituted by equal molar of bicarbonate ion (-0.49±0.04mV, -5.12±0.79μA/cm2, n=16 and -0.64±0.10mV, -6.73±0.98μA/cm2, n=9 respectively). Conclusions: Our results indicate the presence of a non-selective anion pathway in the bovine ciliary epithelium. Chloride and bicarbonate ion may share the same pathway in aqueous humour secretion.