Figure 7.

Analysis of cell cGMP contents by ELISA. (A) Average cell cGMP contents in instilled lungs (left), H441 cells (middle), and oocytes (right). n = 6 lungs, 10 H441 monolayers, and 100 oocytes. **P < 0.01. (B) Divergent regulation of ENaC by CPT-cGMP in oocytes (left) and epithelial cells (right). Heterologous ENaC channels are not regulated by cGMP/PKG and cAMP/PKA pathways. CPT-cGMP therefore does not regulate cloned human ENaC in oocytes via the cGMP/PKG signaling pathway and only serves as an external ligand. This compound stimulates native ENaC function by acting as an external ligand and activating internal PKG in sequence. cGMP is anticipated to accumulate around ENaC as an autocrine.