title: Dopamine regulation of amiloride-sensitive sodium channels in lung cells.
abstract: Dopamine increases lung fluid clearance. This is partly due to activation of basolateral Na-K-ATPase. However, activation of Na-K-ATPase by itself is unlikely to produce large changes in transepithelial transport. Therefore, we examined apical and basolateral dopamine's effect on apical, highly selective sodium channels [epithelial sodium channels (ENaC)] in monolayers of an alveolar type 2 cell line (L2). Dopamine increased channel open probability (P(o)) without changing the unitary current. The D(1) receptor blocker SCH-23390 blocked the dopamine effect, but the D(2) receptor blocker sulpiride did not. The dopamine-mediated increase in ENaC activity was not a secondary effect of dopamine stimulation of Na-K-ATPase, since ouabain applied to the basolateral surface to block the activity of Na-K-ATPase did not alter dopamine-mediated ENaC activity. Protein kinase A (PKA) was not responsible for dopamine's effect since a PKA inhibitor, H89, did not reduce dopamine's effect. However, cpt-2-O-Me-cAMP, which selectively binds and activates EPAC (exchange protein activated by cAMP) but not PKA, increased ENaC P(o). An Src inhibitor, PP2, and the phosphatidylinositol-3-kinase inhibitor, LY-294002, blocked dopamine's effect on ENaC. In addition, an MEK blocker, U0126, an inhibitor of phospholipase A(2), and a protein phosphatase inhibitor also blocked the effect of dopamine on ENaC P(o). Finally, since the cAMP-EPAC-Rap1 pathway also activates DARPP32 (32-kDa dopamine response protein phosphatase), we confirmed that dopamine phosphorylates DARPP32, and okadaic acid, which blocks phosphatases (DARPP32), also blocks dopamine's effect. In summary, dopamine increases ENaC activity by a cAMP-mediated alternative signaling pathway involving EPAC and Rap1, signaling molecules usually associated with growth-factor-activated receptors.
authors.affiliation: Dept. of Physiology, Emory Univ. School of Medicine, 615 Michael St., Atlanta, GA 30322, USA.
authors.forename: My N
authors.initials: MN
authors.lastname: Helms
authors.forename: Xi-Juan
authors.initials: XJ
authors.lastname: Chen
authors.forename: Semra
authors.initials: S
authors.lastname: Ramosevac
authors.forename: Douglas C
authors.initials: DC
authors.lastname: Eaton
authors.forename: Lucky
authors.initials: L
authors.lastname: Jain
mesh_terms: D000818:Animals; D002460:Cell Line; D002867:Chromones / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D004298:Dopamine / Q000494:pharmacology / Q000502:physiology*; D018492:Dopamine Antagonists / Q000494:pharmacology; D051937:Dopamine and cAMP-Regulated Phosphoprotein 32 / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D053503:Epithelial Sodium Channels; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism; D007546:Isoquinolines / Q000494:pharmacology; D008168:Lung / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009025:Morpholines / Q000494:pharmacology; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011650:Pulmonary Alveoli / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017447:Receptors, Dopamine D1 / Q000378:metabolism; D017448:Receptors, Dopamine D2 / Q000378:metabolism; D015222:Sodium Channels / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013449:Sulfonamides / Q000494:pharmacology; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: D002867:Chromones; D018492:Dopamine Antagonists; D051937:Dopamine and cAMP-Regulated Phosphoprotein 32; D004791:Enzyme Inhibitors; D053503:Epithelial Sodium Channels; D007546:Isoquinolines; D009025:Morpholines; D000081082:Phosphoinositide-3 Kinase Inhibitors; C497930:Ppp1r1b protein, rat; D047428:Protein Kinase Inhibitors; D017447:Receptors, Dopamine D1; D017448:Receptors, Dopamine D2; D015222:Sodium Channels; D013449:Sulfonamides; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D000242:Cyclic AMP; D019061:src-Family Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D010744:Phosphoric Monoester Hydrolases; D019205:GTP-Binding Protein alpha Subunits, Gs; D000254:Sodium-Potassium-Exchanging ATPase; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; D004298:Dopamine