adrenomedullin and 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.

Topics: 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; Adrenal Medulla; Adrenomedullin; Bronchi; Cells, Cultured; Chloride Channels; Cyclic AMP; Epithelial Cells; Gastrointestinal Hormones; Humans; Natriuretic Peptides; Neuropeptides; Patch-Clamp Techniques; Peptides; Pituitary Adenylate Cyclase-Activating Polypeptide; Secretin; Thionucleotides

Smooth muscle cells isolated from the caecal circular smooth muscle layers of the guinea pig were used to determine whether adrenomedullin and guanylin can inhibit the contractile response produced by 10(-9) M cholecystokinin octapeptide (CCK-8). In addition, to elucidate each intracellular mechanisms, we examined the effects of an inhibitor of cAMP-dependent protein kinase, an inhibitor of particulate guanylate cyclase, and an inhibitor of soluble guanylate cyclase on the adrenomedullin- or guanylin-induced relaxation of the caecal circular smooth muscle cells. Both adrenomedullin and guanylin inhibited the contractile response produced by CCK-8 in a dose-dependent manner, with IC50 values of 0.12 nM and 2.4 pM, respectively. An inhibitor of cAMP-dependent protein kinase significantly inhibited the relaxation produced by adrenomedullin. In contrast, an inhibitor of particulate guanylate cyclase and an inhibitor of soluble guanylate cyclase did not have any significant effect on the relaxation produced by adrenomedullin. On the other hand, an inhibitor of particulate guanylate cyclase significantly inhibited the guanylin-induced relaxation, although an inhibitor of cAMP-dependent protein kinase and an inhibitor of soluble guanylate cyclase did not have any significant effect on the guanylin-induced relaxation. In this study, we first demonstrated the direct inhibitory effects of adrenomedullin via cAMP system and guanylin via particulate guanylate cyclase system on the isolated caecal circular smooth muscle cells.

Topics: Adrenomedullin; Animals; Cecum; Dose-Response Relationship, Drug; Gastrointestinal Hormones; Guinea Pigs; Humans; In Vitro Techniques; Male; Muscle, Smooth; Natriuretic Peptides; Peptides; Vasodilator Agents