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King Wah Angela Cheng, King Kit Li, Chi Ho To, Chi Wai Do; cAMP Promotes Fluid Transport Across Porcine Ciliary Epithelium By Enhancing Gap Junctional Permeability. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5332.
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To determine the effect of cAMP on fluid transport across porcine ciliary epithelium.
Electrical parameters including transepithelial potential difference (PD), short-circuit current (Isc) and transmural resistance (Rt) were continuously monitored in modified Ussing-Zhrahn-type chamber. Lucifier Yellow dye transfer technique was employed to study the gap junctional permeability. Whole-cell patch clamp recording was used to study Cl- channel activity.
The addition of 1-100 μM 8-bromo-cAMP to the aqueous surface consistently stimulated Isc by 60-80% across porcine ciliary epithelium. This effect was completely abolished by either bathing Cl- substitution or pretreatment with 3.5 mM heptanol (a gap junction blocker), indicating that NPE-Cl- channels and/or gap junctions between PE and NPE are the possible cellular site(s) of cAMP-induced responses. Addition of 10 μM 8-bromo-cAMP significantly increased the rate of Lucifier Yellow dye transfer from PE to NPE cell in isolated porcine PE-NPE cell couplets (n=24; p<0.05). However, cAMP had no effect on whole-cell Cl- current in both isolated native PE (n=4) and NPE (n=7) cells.
Our results suggest that cAMP stimulates Isc primarily by increasing the gap junctional permeability between PE and NPE cells. In the absence of gap junctions linking the two cell layers, the effects of cAMP on Cl- efflux are, however, subtle in both cell types.
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