Regulation of I(Ks) Potassium Current by Isoproterenol in Adult Cardiomyocytes Requires Type 9 Adenylyl Cyclase.

The subunits KCNQ1 and KCNE1 generate the slowly activating, delayed rectifier potassium current, I(Ks), that responds to sympathetic stimulation and is critical for human cardiac repolarization. The A-kinase anchoring protein Yotiao facilitates macromolecular complex formation between I(Ks) and protein kinase A (PKA) to regulate phosphorylation of KCNQ1 and I(Ks) currents following beta-adrenergic stimulation. We have previously shown that adenylyl cyclase Type 9 (AC9) is associated with a KCNQ1-Yotiao-PKA complex and facilitates isoproterenol-stimulated phosphorylation of KCNQ1 in an immortalized cell line. However, requirement for AC9 in sympathetic control of I(Ks) in the heart was unknown. Using a transgenic mouse strain expressing the KCNQ1-KCNE1 subunits of I(Ks), we show that AC9 is the only adenylyl cyclase (AC) isoform associated with the KCNQ1-KCNE1-Yotiao complex in the heart. Deletion of AC9 resulted in the loss of isoproterenol-stimulated KCNQ1 phosphorylation in vivo, even though AC9 represents less than 3% of total cardiac AC activity. Importantly, a significant reduction of isoproterenol-stimulated I(Ks) currents was also observed in adult cardiomyocytes from I(Ks)-expressing AC9KO mice. AC9 and Yotiao co-localize with N-cadherin, a marker of intercalated disks and cell-cell junctions, in neonatal and adult cardiomyocytes, respectively. In conclusion, AC9 is necessary for sympathetic regulation of PKA phosphorylation of KCNQ1 in vivo and for functional regulation of I(Ks) in adult cardiomyocytes.