The airway-epithelium: a novel site of action by guanylin

We studied the activation of a chloride channel in normal human bronchial epithelial cells (NHBE) by guanylin. We have observed a background Cl current (ICl,background) and a guanylin-induced outward rectifying chloride currents (ORCC) in NHBE. ICl,background was present in 93% of cells (n = 114), was outwardly-rectifying, and could be completely blocked by 100 microM NPPB (5-Nitro-2(3-phenyl-propylamino)-benzoic acid. Activation of cAMP-activated Cl current with 200 microM CPT-cAMP (8-(4-Chlorophenylthio) adenosine-3',5'-monophosphate) occurred in only 35.3% of cells (n = 34). Gyanylin activated an ORCC in 78.6% (n = 11) of cells. Gyanylin also induced chloride currents in cells that had failed to respond to CPT-cAMP (n = 5). Both CPT-cAMP and the guanylin-induced chloride currents showed strong outward rectification. 500 microM DIDS (4,4'-diisothiocyanostibene-2,2'-disulfonic acid) blocked the guanylin-induced ORCC (n = 10).

Guanylin activates a DIDS-sensitive ORCC in the NHBE cell which is only modestly activated by cAMP. The guanylin receptor in the NHBE might be of major importance in the regulation of chloride channel activity and transepithelial fluid transport in normal and abnormal airways.