Atrial natriuretic peptide modulates alveolar type 2 cell adenylyl and guanylyl cyclases and inhibits surfactant secretion

Alveolar epithelial type 2 (T2) cells isolated from the lungs of adult rats responded to exogenous atrial natriuretic peptide (ANP) by two signalling mechanisms. First, ANP induced a dose-dependent reduction of ligand-stimulated adenylyl cyclase activity and cAMP accumulation. This effect was inhibited by the addition of GDPβS or by pretreatment with pertussis toxin (PT), consistent with mediation by a Gi protein(s). PT- catalyzed [³²P]ADP-ribosylation, immunoblots with specific antisera, and Northern blot analysis demonstrated that T2 cells contain the G-proteins Gi₂ and Gi₃ which could transduce this signal. ANP also promoted PT- insensitive, dose-dependent accumulation of cGMP, consistent with activation of a receptor guanylyl cyclase. Isoproterenol-stimulated phosphatidylcholine secretion was markedly attenuated by ANP, and this effect was inhibited by PT pretreatment, consistent with mediation by a Gi protein(s). These data indicate that in addition to the lung being a major clearance organ for circulating ANP, lung parenchymal cells are targets of ANP action.