Purpose The role played by cAMP, an important second intracellular messenger, in aqueous humor formation of the eye is still unclear. This study was to investigate how cAMP modulates short-circuit current (Isc) in isolated human ciliary processes and the possible involvement of chloride transport across the tissue in cAMP-induced Isc change.
Methods In an Ussing-type chamber system, the Isc changes induced by the cAMP analogue 8-bromo-cAMP and an adenylyl cyclase activator forskolin in isolated human ciliary processes were assessed. The involvement of Cl- component in the bath solution was investigated. The effect of Cl- channel (10 mmol/l niflumic acid, 1 mmol/l DIDS), K+-channel (10 mmol/l TEA) or Na+-channel blockers (1 mmol/l amiloride) on 8-bromo-cAMP-induced Isc change was also studied.
Results Dose-dependently, 8-bromo-cAMP (10 nmol/l-30 mmol/l) or forskolin (10 nmol/l-3 mmol/l) increased Isc across the ciliary processes with an increase in negative potential difference on the non-pigmented epithelium side of the tissue. Isc increase induced by 8-bromo-cAMP was more pronounced when the drug was applied on the NPE than on the PE side. When bathed the tissue with low Cl- solutions, the Isc increase was significantly inhibited. Finally, niflumic acid and DIDS, but not TEA and amiloride, significantly prevented the Isc increase induced by 8-bromo-cAMP.
Conclusions 8-bromo-cAMP stimulates stroma-to-aqueous anionic transport in isolated human ciliary processes. Chloride is likely to be among the ions whose transportation across the tissue is triggered by cAMP, suggesting the potential role of cAMP in the process of aqueous humor formation in human eyes. |
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