Epithelial sodium channels expressed in Xenopus oocytes are activated by cyclic-AMP

Academic Article

Abstract

  • Background. The regulation of the epithelial sodium channel (ENaC) is a key determinant of sodium homeostasis. The effect of cyclic AMP (cAMP) on ENaC activity is tissue-specific, and is controversial when ENaC is expressed in Xenopus oocytes. Methods. The modulation of ENaC by cAMP in oocytes expressing human or rat ENaC was performed with two-electrode voltage clamping. Results. 250μM 8-(4-chlorophenylthio)-adenosine 3′, 5′-cyclic monophosphate (8-CPT-cAMP) added to the bath significantly increased normalized amiloride-sensitive currents within 60s in oocytes expressing human α, β, and γ subunits (5ng cRNA each). The cAMP effect was dose-dependent and was partially inhibited by 200μM Rp-CPT-cAMP, a competitive cAMP antagonist. A transient effect of 8-CPT-cAMP on rat ENaC activity was also observed. Oocytes expressing rat α subunits with γ subunits (which have a putative protein kinase A phosphorylation site) showed similar increases in amiloride-sensitive current with 250μM 8-CPT-cAMP, while oocytes expressing rat α sub-units with β subunits were not activated by 8-CPT-cAMP. Further, rat ENaC (but not human ENaC)-expressing oocytes were not activated by cAMP when oocytes were continuously superfused during electrophysiological recordings, suggesting that rat ENaC activation by cAMP is dependent upon the condition of oocytes during cAMP stimulation. Conclusion. The present results suggest that ENaC expressed in Xenopus oocytes can be activated by cAMP, and that the γ subunit confers sensitivity to cAMP modulation of rat ENaC activity.
  • Authors

    Published In

    Digital Object Identifier (doi)

    Author List

  • Tamba K; Oh YS; Tucker JK; Quick MW; Warnock DG
  • Start Page

  • 195
  • End Page

  • 201
  • Volume

  • 6
  • Issue

  • 4