Effects of PKA inhibitors, H-compounds, on epithelial Na+ channels via PKA-independent mechanisms

The Na+ transport in alveolar type II epithelial cells of rat fetal lung was stimulated by cAMP, which is generally thought to act through activation of protein kinase A (PKA). PKA inhibitors (H8, H89 and H7) stimulated amiloride-sensitive Na+ transport in the alveolar type II epithelial cells. H85, an inactive form of H89 as a PKA Inhibitor, had also mimicked the stimulatory action of H89 on the Na+ transport. On the other hand, another type of PKA Inhibitor, KT5720 or myristoylated PKA inhibitory peptide [14-22] amide, did not stimulate the Na+ transport, but inhibited the Na+ transport unlike H-compounds. These observations suggest that H-compounds act on the Na+ transport depending on the structure.