Role of ATP-dependent K+ channels in the electrical excitability of early embryonic stem cell-derived cardiomyocytes

Single, murine embryonic stem cell-derived early stage cardiomyocytes disso ciated from embryoid bodies expressed two inward rectifier K+ channels, I-K 1 and the ATP dependent K+ current. I-K1 exhibited low density in early sta ge cardiomyocytes, but increased significantly in late stage cells. In cont rast, the ATP dependent K+ current was expressed at similar densities in ea rly and late stage cardiomyocytes. This current was found to be involved in the determination of the membrane potential, since glibenclamide depolariz ed early cardiomyocytes and exerted a positive chronotropic effect. Some ca rdiomyocytes displayed a bursting behavior of action potentials, characteri zed by alternating periods with and without action potentials. During the p hases without action potentials, the membrane potential was hyperpolarized, indicating the involvement of K+ channels in the generation of this bursti ng behavior. Extracellular recording techniques were applied to spontaneous ly contracting areas of whole embryoid bodies. In 20% of these bursting beh avior similar to that seen in the single cells was observed. In regularly b eating embryoid bodies, bursting could be induced by reduction of substrate s from the extracellular medium as well as by superfusion with the positive chronotropic agents Bay K 8644 or isoproterenol. Perfusion with substrate- reduced medium induced bursting behavior after a short latency, isoproteren ol and Bay K 8644 resulted in a positive chronotropic response followed by bursting behavior with longer latencies. The spontaneous bursting was block ed by glibenclamide. These experimental results suggest that intermittent a ctivation of ATP dependent K+ channels underlies the bursting behavior obse rved in single cardiomyocytes and in the whole embryoid body. Conditions of metabolic stress lead to the rhythmic suppression of action potential gene ration. Our data indicate that ATP dependent K+ channels play a prominent r ole in the cellular excitability of early cardiomyocytes.