Regulation of chloride channel trafficking by cyclic AMP via protein kinase A-independent pathway in A6 renal epithelial cells.

The apical membrane of renal epithelial A6 cells has 3 and 8 pS Cl- channels. Both types of the channels were blocked by NPPB (5-Nitro-2-(3-phenylpropylamino)-benzoic acid; 100 microM). 8-bromo-cAMP (Br-cAMP) increased the open probability of 3 pS Cl- channel and this action was inhibited by pretreatment with H89, an inhibitor of cAMP-dependent protein kinase (PKA). On the other hand, the number of 8 pS Cl- channel was increased by Br-cAMP. The increase in number of 8 pS Cl- channel by Br-cAMP was inhibited by brefeldin A (a blocker of movement of membrane protein from an intracellular pool to the cell surface) but not by H89. These observations indicate that cAMP could activate the 3 pS Cl- channel through PKA-dependent phosphorylation, and that cAMP could stimulate translocation of the 8 pS Cl- channel through PKA-independent pathways. We conclude that PKA-independent pathways are involved in cAMP signaling mechanisms in addition to PKA-dependent pathways.