title: Osmotic regulation of Na+ transport across A6 epithelium: interactions with prostaglandin E2 and cyclic AMP.
abstract: Previous work from this laboratory has shown that apical membrane sodium channel activity is stimulated by serosal hyposmotic solutions (Wills, Millinoff & Crowe, 1991). In the present study, we determined whether this stimulation of sodium transport is additive with the actions of prostaglandin E2 (PGE2) or cyclic AMP (cAMP). Addition of exogenous PGE2 (100 nM; serosal bath) to isosmotic solutions led to large increases in the amiloride-sensitive short-circuit current (Isc) and transepithelial conductance (Gt), whereas no significant effects of PGE2 were observed in hyposmotic serosal solutions. Subsequent addition of mucosal amiloride reduced Isc by approximately 95% and Gt by approximately 60%. Inhibition of endogenous PGE2 production by blockers of phospholipase A2 activity (quinacrine or 3[4-octadecyl]-benzoylacrylic acid; OBBA), or inhibition of cyclooxygenase activity by indomethacin reduced the stimulation of Isc and Gt by hyposmotic solutions. Addition of forskolin (FSK) or 3-Isobutyl-1-methylxanthine (IBMX) also resulted in approximately twofold increases in the amiloride-sensitive Isc and Gt and abolished the effects of subsequent hyposmotic challenge. The effects of forskolin, PGE2, and hyposmotic challenge were diminished by pretreatment with H89, a protein kinase A (PKA) inhibitor. We conclude that osmotic regulation of sodium channel activity interacts with multiple intracellular signaling pathways, specifically the arachidonic acid metabolic pathway and the cAMP/PKA intracellular messenger cascade.
authors.affiliation: Department of Physiology & Biophysics, University of Texas Medical Branch, Galveston 77555, USA.
authors.forename: P S
authors.initials: PS
authors.lastname: Matsumoto
authors.forename: L
authors.initials: L
authors.lastname: Mo
authors.forename: N K
authors.initials: NK
authors.lastname: Wills
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D015232:Dinoprostone / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000494:pharmacology; D004789:Enzyme Activation; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D009994:Osmolar Concentration; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D015222:Sodium Channels / Q000378:metabolism*; D012996:Solutions; D014882:Water-Electrolyte Balance
chemical_list: D010726:Phosphodiesterase Inhibitors; D015222:Sodium Channels; D012996:Solutions; D005576:Colforsin; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D000262:Adenylyl Cyclases; D015232:Dinoprostone; D015056:1-Methyl-3-isobutylxanthine