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Ying Ni, Renyi Wu, Wen Xu, Helmut Maecke, Josef Flammer, Ivan O. Haefliger; Effect of cAMP on Porcine Ciliary Transepithelial Short-Circuit Current, Sodium Transport, and Chloride Transport. Invest. Ophthalmol. Vis. Sci. 2006;47(5):2065-2074. doi: 10.1167/iovs.05-0228.
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purpose. To investigate the effects of 8-bromo-cAMP (cAMP) on porcine ciliary transepithelial short-circuit current (Isc) and transport of chloride (Cl−) and sodium (Na+).
methods. With Ussing-type chambers, cAMP-induced changes in Isc, electrical resistance (ER), and transepithelial 36Cl− and 22Na+ fluxes were measured. Drugs were applied to the nonpigmented epithelium (NPE) and/or pigmented epithelium (PE) side(s). The effect of IBMX (1, 5, or 10 μM; 3-isobutyl-1-methylxanthine) on Isc-increase induced by 8-bromo-cAMP on the PE side was also tested.
results. On the NPE side, a single concentration (10 μM, 100 μM, or 1 mM) of 8-bromo-cAMP induced a biphasic (transient peak followed by sustained plateau) Isc increase. On the PE side, 8-bromo-cAMP induced a similar but delayed biphasic Isc increase at 1 mM, a slight plateau-Isc increase at 100 μM, and no Isc increase at 10 μM. In the concentration–response curve, the cAMP-induced peak-Isc increase became significant at a concentration 10,000 times lower on the NPE than on the PE side. At 10 μM, the cumulative cAMP-induced Isc-increase reached its maximum on the NPE side, but was virtually nonexistent on the PE side. IBMX (a phosphodiesterase inhibitor) but not 8-CPT-6-Phe-cAMP (higher permeability than 8-bromo-cAMP) significantly increased the peak-Isc concentration–response curve induced by 8-bromo-cAMP (10 nM–1 mM) on the PE side. On the NPE but not the PE side, 10 μM 8-bromo-cAMP induced a significant but transient increase in net PE-to-NPE 36Cl− flux (1.03 ± 0.18 μEq/min per square centimeter; P < 0.001). Neither ER nor transepithelial 22Na+ flux was changed after cAMP exposure.
conclusions. In porcine ciliary processes, apparently on the NPE side, cAMP triggers a biphasic (transient peak followed by a sustained plateau) Isc increase. Only the peak-Isc increase involves an increase in net PE-to-NPE Cl− transport.
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