0443 : In vitro reconstruction of an arrhythmic phenotype using cardiac-pacemaker-like cells differentiated from muscle derived stem cells

Skeletal Muscle Derived Stem Cells (MDSC), spontaneously differentiate in vitro into multiple cell types such as myocytes, adipocytes, smooth muscle, neuronal and cardiac cells. We characterize here a sub-population of in vitro differentiated MDSC, hereby named Muscle Derived PaceMaker-like cells (MDPMc) displaying cardiac phenotype, spontaneous automaticity and contractile activity. We used patch-clamp recordings of ionic currents, imaging of spontaneous intracellular calcium transients, and measurements of contraction velocity and immuno-fluorescence detection of ion channel proteins to determine the functional properties shared by MDPMc and native cardiac pacemaker cells. Functional analysis of MDPMc differentiated from knockout mice lacking L-type Cav1.3 Ca2+ channels or G-protein activated K+ (GIRK4, underlying the muscarinic activated IKACh current) channels showed that MDPMc display similar functional properties to native sino-atrial mutant cells. Similarly to what observed in native sino-atrial Cav1.3-/- cells, MDPMc differentiated from Cav1.3-/- mice displayed reduction in the spontaneous beating rate of 26,6%±9,91 (n=9) compared to that recorded in MDPMc differentiated from wild-type mice. Acetylcholine (10nM) decreased the contraction velocity of wild-type MDPMc by 62,47%±13,75 (n=12), but only by 14,95%±5,96 (n=8) in MDPMc derived Girk4-/- mice, values that were comparable to those observed in native Girk4-/- sino-atrial cells. MDPMc expressed the hyperpolarization-activated HCN4 channel, a key marker of pacemaker cells. The HCN channel inhibitor ivabradine 1μm slowed the spontaneous beating rate of MDPMc by 53,05%±11,67 (n=19) demonstrating that these cells exhibited automaticity similar to that of native pacemaker cells. Finally, we were able to derive MDPMc also from the primate mouse lemur. In conclusion, we show that MDPMc may be used as a new cellular model recapitulating dysfunction of heart automaticity and arrhythmias