AKAP proteins anchor cAMP-dependent protein kinase to KvLQT1/IsK channel complex

In cardiac myocytes, the slow component of the delayed rectifier K⁺ current (I_Ks) is regulated by cAMP. Elevated cAMP increases I_Ks amplitude, slows its deactivation kinetics, and shifts its activation curve. At the molecular level, I_Ks channels are composed of KvLQT1/IsK complexes. In a variety of mammalian heterologous expression systems maintained at physiological temperature, we explored cAMP regulation of recombinant KvLQT1/IsK complexes. In these systems, KvLQT1/IsK complexes were totally insensitive to cAMP regulation. cAMP regulation was not restored by coexpression with the dominant negative isoform of KvLQT1 or with the cystic fibrosis transmembrane regulator. In contrast, coexpression of the neuronal A kinase anchoring protein (AKAP)79, a fragment of a cardiac AKAP (mAKAP), or cardiac AKAP15/18 restored cAMP regulation of KvLQT1/IsK complexes inasmuch as cAMP stimulation increased the/I_Ks amplitude, increased its deactivation time constant, and negatively shifted its activation curve. However, in cells expressing an AKAP, the effects of cAMP stimulation on the I_Ks amplitude remained modest compared with those previously reported in cardiac myocytes. The effects of cAMP stimulation were fully prevented by including the Ht31 peptide (a global disruptor of protein kinase A anchoring) in the intracellular medium. We concluded that cAMP regulation of I_Ks requires protein kinase A anchoring by AKAPs, which therefore participate with the channel protein complex underlying I_Ks.