OSMOTIC REGULATION OF NA- INTERACTIONS WITH PROSTAGLANDIN E-2 AND CYCLIC-AMP( TRANSPORT ACROSS A6 EPITHELIUM )

Previous work from this laboratory has shown that apical membrane sodi um channel activity is stimulated by serosal hyposmotic solutions (Wil ls, Millinoff & Crowe, 1991). In the present study, we determined whet her this stimulation of sodium transport is additive with the actions of prostaglandin E-2 (PGE(2)) or cyclic AMP (cAMP). Addition of exogen ous PGE(2) (100 nM; serosal bath) to isosmotic solutions led to large increases in the amiloride-sensitive short-circuit current (I-sc) and transepithelial conductance (G(t)), whereas no significant effects of PGE(2) were observed in hyposmotic serosal solutions. Subsequent addit ion of mucosal amiloride reduced I-sc by similar to 95% and G(t) by si milar to 60%. Inhibition of endogenous PGE(2) production by blockers o f phospholipase A(2) activity (quinacrine or 3[4-octadecyl]-benzoylacr ylic acid; OBBA), or inhibition of cyclooxygenase activity by indometh acin reduced the stimulation of I-sc and GI by hyposmotic solutions. A ddition of forskolin (FSK) or 3-Isobutyl-1 -methylxanthine (IBMX) also resulted in approximately twofold increases in the amiloride-sensitiv e I-sc and G(t) and abolished the effects of subsequent hyposmotic cha llenge. The effects of forskolin, PGE(2), and hyposmotic challenge wer e diminished by pretreatment with H89, a protein kinase A (PKA) inhibi tor. We conclude that osmotic regulation of sodium channel activity in teracts with multiple intracellular signaling pathways, specifically t he arachidonic acid metabolic pathway and the cAMP/PKA intracellular m essenger cascade.