ATRIAL-NATRIURETIC-PEPTIDE STIMULATES CL- TRANSPORT IN RETINAL-PIGMENT EPITHELIAL-CELLS

To study the regulatory role of atrial natriuretic peptide (ANP) on the Cl- transport activity of retinal pigment epithelial (RPE) cells, RPE cells from rabbits were cultured and exposed to ANP and other reagents under perfusion. The changes in intracellular Cl- concentration ([Cl-](i)) were continuously recorded using a Cl--sensitive fluorescent dye. The cGMP content was estimated by radioimmunoassay. ANP increased the cGMP content and the [Cl-](i) in RPE cells. A guanylate cyclase activator, nitric oxide, and a cell permeable cGMP precursor, 8-Br-cGMP, also increased the level of cGMP and the [Cl-](i). A guanylate cyclase inhibitor, LY83583, an inhibitor of cGMP-dependent protein kinase, KT5823, and an inhibitor of Na+/K+/2Cl(-) cotransporter, bumetanide, diminished or abolished the ANP-induced increase in [Cl-](i). ANP facilitates Cl- accumulation in RPE cells, which is mediated by guanylate cyclase, cGMP-dependent protein kinase, and the Na+/K+/ 2Cl(-) cotransporter.