Probably targets cAMP-dependent protein kinase (PKA) to the cellular membrane or cytoskeletal structures. The membrane-associated form reduces epithelial sodium channel (ENaC) activity, whereas the free cytoplasmic form may negatively regulate ENaC channel feedback inhibition by intracellular sodium (By similarity). Isoform Delta may be involved in shuttling aquaporin-2 (AQP2) to the plasma membrane. Binds cAMP-dependent protein kinase (PKA). Interacts with PRKCA; only the cytoplasmic form is capable of interacting with PRKCA. Cotranslocates with AQP2 to the plasma membrane in response to arginine-vasopressin (AVP) stimulation in inner medullary collecting duct (IMCD) cells. Expressed highly in the heart, and moderately in brain, lung, liver, kidney and testis. Hardly detectable in spleen and skeletal muscle. In kidney, isoform Delta is expressed in the principal cells of the IMCD.