Abstract
A major mechanism for Na^+^ transport across epithelia occurs through epithelial Na^+^ channels (ENaC). ENaC is a multimeric channel consisting of three subunits (α, β, and γ). The α‐subunit is critical for ENaC function. In specific culture conditions, the rat submandibular gland epithelial cell line (SMG‐C6) demonstrates minimal Na^+^ transport properties and exposure to dibutyryl cAMP (DbcAMP) for up to 48 h caused an elevation of α‐ENaC mRNA and protein expression and amiloride‐sensitive short‐circuit current (I~SC~). Here we examined the early signaling pathways evoked by DbcAMP which contribute to the eventual increase in Na^+^ transport is present. Treatment with either of the protein kinase A (PKA) inhibitors KT5720 or H‐89 followed by exposure to 1 mM DbcAMP for 24 h markedly attenuated DbcAMP‐induced α‐ENaC protein formation and I~SC~. Exposure of SMG‐C6 cells to 1 mM DbcAMP induced a rapid, transient phosphorylation of the cAMP response element binding protein (CREB). This response was attenuated in the presence of either KT5720 or H‐89. Dominant‐negative CREB decreased DbcAMP‐induced α‐ENaC expression. Suppression of the extracellular signal‐regulated protein kinase (ERK 1,2) with PD98059 or the p38 mitogen‐activated protein kinase (MAPK) pathway with SB203580 reduced DbcAMP‐induced α‐ENaC protein levels in SMG‐C6 cells. DbcAMP‐induced phosphorylation of CREB was markedly attenuated by PD98059 or SB203580. DbcAMP‐induced activation of the either the p38 or the ERK 1,2 MAPK pathways was abolished by either of the PKA inhibitors, H‐89 or KT5720. Cross talk between these signaling pathways induced by DbcAMP via the activation of CREB appears to contribute to increased levels of α‐ENaC observed after 24 h of treatment in SMG‐C6 epithelial cells. J. Cell. Physiol. 215: 101–110, 2008. © 2007 Wiley‐Liss, Inc.