Cardiomyocytes from AKAP7 knockout mice respond normally to adrenergic stimulation

Abstract

Protein kinase A (PKA) is activated during sympathetic stimulation of the heart and phosphorylates key proteins involved in cardiac Ca2+ handling, including the L-type Ca2+ channel (CaV1.2) and phospholamban (PLN). This results in acceleration and amplification of the beat-to-beat changes in cytosolic Ca2+ in cardiomyocytes and, in turn, an increased rate and force of contraction. PKA is held in proximity to its substrates by protein scaffolds called A kinase anchoring proteins (AKAPs). It has been suggested that the short and long isoforms of AKAP7 (also called AKAP15/18) localize PKA in complexes with CaV1.2 and PLN, respectively. We generated an AKAP7 KO mouse in which all isoforms were deleted and tested whether Ca2+ current, intracellular Ca2+ concentration, or Ca2+ reuptake were impaired in isolated adult ventricular cardiomyocytes following stimulation with the β-adrenergic agonist isoproterenol. KO cardiomyocytes responded normally to adrenergic stimulation, as measured by whole-cell patch clamp or a fluorescent intracellular Ca2+ indicator. Phosphorylation of CaV1.2 and PLN were also unaffected by genetic deletion of AKAP7. Immunoblot and RT-PCR revealed that only the long isoforms of AKAP7 were detectable in ventricular cardiomyocytes. The results indicate that AKAP7 is not required for regulation of Ca2+ handling in mouse cardiomyocytes.