A-KINASE ANCHORING PROTEIN-100 (AKAP100) IS LOCALIZED IN MULTIPLE SUBCELLULAR COMPARTMENTS IN THE ADULT-RAT HEART

Stimulation of beta-adrenergic receptors activates type I and II cycli c AMP-dependent protein kinase A, resulting in phosphorylation of vari ous proteins in the heart. It has been proposed that PKA II compartmen talization by A-kinase-anchoring proteins (AKAPs) regulates cyclic AMP -dependent signaling in the cell. We investigated the expression and l ocalization of AKAP100 in adult hearts. By immunoblotting, we identifi ed AKAP100 in adult rat and human hearts, and showed that type I and I I regulatory (RI and II) subunits of PKA are present in the rat heart. By immunofluorescence and confocal microscopy of rat cardiac myocytes and cryostat sections of rat left ventricle papillary muscles, we loc alized AKAP100 to the nucleus,sarcolemma, intercalated disc. and at th e level of the Z-line. After double immunostaining of transverse cross -sections of the papillary muscles with AKAP100 plus alpha-actinin-spe cific antibodies or AKAP100 plus ryanodine receptor-specific antibodie s, confocal images showed AKAP100 localization at the region of the tr ansverse tubule/junctional sarcoplasmic reticulum. RI is distributed d ifferently from RII in the myocytes. RII, but not RI, was colocalized with AKAP100 in the rat heart. Our studies suggest that AKAP100 tether s PKA II to multiple subcellular compartments for phosphorylation of d ifferent pools of substrate proteins in the heart.