PURPOSE. To investigate the potential significance of cAMP in the regulation of Cl- transport across the bovine ciliary body/epithelium (CBE). METHODS. Fresh native bovine CBE preparation was mounted in a modified Ussing chamber. The effects of cAMP-stimulating agents on short-circuit current (Isc) and net 36Cl- secretion were determined. RESULTS. Addition of cAMP-stimulating agents inhibited net Cl- secretion. Forskolin, when added bilaterally, reduced Cl- secretion by 60%. Similarly, bilateral isoproterenol or vasoactive intestinal peptide inhibited Cl- transport by 15% and 37%, respectively, suggesting a cAMP-sensitive Cl- transport across the ciliary epithelium. This notion was supported by the exogenous application of 8-bromo-cAMP (8-Br-cAMP) or 3-isobutyl-1-methylxanthine (IBMX), which reduced the net Cl- secretion by 49% and 85%, respectively. In unstimulated preparations, addition of 5-nitro-2(3-phenylpropylamino)-benzoic acid (NPPB) to the blood side had no effects on Isc and net Cl- transport, indicating that Cl- reabsorption was negligible under baseline conditions. Also, pretreatment with NPPB from the blood side did not prevent forskolin-induced Isc inhibition, suggesting that the inhibition of Cl- transport did not result from the facilitation of Cl- reabsorption. However, pretreatment with heptanol from both sides completely blocked the forskolin-induced Isc inhibition, suggesting that cAMP may reduce Cl- transport by uncoupling the intercellular gap junctions. CONCLUSIONS. The results suggest that cAMP plays a crucial role in modulating Cl- secretion across the ciliary epithelium. The effect is possibly mediated, at least in part, by the regulation of the permeability of gap junctions between pigmented and nonpigmented ciliary epithelial cells.
ASJC Scopus subject areas
- Sensory Systems
- Cellular and Molecular Neuroscience