Prolonged repolarization and triggered activity induced by adenoviral expression of HERG N629D in cardiomyocytes derived from stem cells

The long QT syndrome, N629D HERG mutation, alters the pore selectivity signature sequence, GFGN to GFGD. Heterologous co-expression of N629D and the wildtype HERG resulted in a relative loss of the selectivity of K+ over Na+, but its physiologic relevance has not been assessed in cardiac myocytes. Accordingly, N629D was overexpressed, via adenoviral gene transfer, in cardiomyocytes derived from mouse stem cells. Three IKr phenotypes were observed: (1) the wildtype-like IKr showed inward rectification and a positive tail current; (2) the N629D-like IKr showed outward rectification and an inward tail current; and (3) intermediate IKr showed a small outward tail current. Action potentials (AP) were paired with the IKr measurements in each cell. Resting membrane potential (RMP) was critically dependent on the IKr phenotype. The resting membrane potential of the cells was -61 +/- 5 mV (n=40) in wildtype, -63 +/- 3 mV (n=18) in wildtype-like IKr phenotype, -30 +/- 2 mV (n=12) in N629D-like and -47 +/- 2 mV (n=24) in intermediate phenotype (p