cAMP stimulates Na(+) transport in rat fetal pneumocyte: involvement of a PTK- but not a PKA-dependent pathway.
To study a cAMP-mediated signaling pathway in the regulation of amiloride-sensitive Na(+) transport in rat fetal distal lung epithelial cells, we measured an amiloride-sensitive short-circuit current (Na(+) transport). Forskolin, which increases the cytosolic cAMP concentration, stimulated the Na(+) transport. Forskolin also activated cAMP-dependent protein kinase (PKA). A beta-adrenergic agonist and cAMP mimicked the forskolin action. PKA inhibitors KT-5720, H-8, and myristoylated PKA-inhibitory peptide amide-(14-22) did not influence the forskolin action. These results suggest that forskolin stimulates Na(+) transport through a PKA-independent pathway. Furthermore, forskolin increased tyrosine phosphorylation of approximately 70- to 80-, approximately 97-, and approximately 110- to 120-kDa proteins. Protein tyrosine kinase (PTK) inhibitors (tyrphostin A23 and genistein) abolished the forskolin action. Moreover, 5-nitro-2-(3-phenylpropylamino)benzoate (a Cl(-)-channel blocker) prevented the stimulatory action of forskolin on Na(+) transport via abolishment of the forskolin-induced cell shrinkage and tyrosine phosphorylation. Based on these results, we conclude that forskolin (and cAMP) stimulates Na(+) transport in a PTK-dependent but not a PKA-dependent pathway by causing cell shrinkage, which activates PTK in rat fetal distal lung epithelial cells.
Niisato
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N
Lung and Cell Biology, Medical Research Council Group in Lung Development, Department of Pediatrics, Institute of Medical Science, The Hospital for Sick Children Research Institute, University of Toronto Faculty of Medicine, Toronto, Ontario, Canada.
Ito
Y
Y
Marunaka
Y
Y
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002412:Cations / Q000378:metabolism; D002478:Cells, Cultured; D018118:Chloride Channels / Q000037:antagonists & inhibitors; D000242:Cyclic AMP / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D004553:Electric Conductivity; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005333:Fetus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D007473:Ion Channels / Q000037:antagonists & inhibitors / Q000187:drug effects; D008168:Lung / Q000196:embryology*; D009579:Nitrobenzoates / Q000494:pharmacology; D019000:Phosphotyrosine / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism*
D002412:Cations; D018118:Chloride Channels; D004791:Enzyme Inhibitors; D007473:Ion Channels; D009579:Nitrobenzoates; D019000:Phosphotyrosine; C058176:5-nitro-2-(3-phenylpropylamino)benzoic acid; D000584:Amiloride; D012964:Sodium; D000242:Cyclic AMP; D011505:Protein-Tyrosine Kinases; D017868:Cyclic AMP-Dependent Protein Kinases