Figure 2.

In Vitro Differentiation Potential of ISL1⁺ HVPs

(A–D) Day 15+ HVPs were analyzed for ventricular markers: (A) MLC2v and cTnT; (B) cTnI; (C) pacemaker marker HCN4; and (D) atrial marker MLC2a. Scale bar, 20 μm. (E and F) Optical recordings of spontaneous (E) and paced (F) day 18 HVP cells. Isochrome maps at 20-ms intervals show spontaneous action potential initiation. The white asterisk represents the origin of point electrical stimulation. (G and H) Optical recordings of spontaneous (G) and paced (H) calcium transients in day 18 HVP cells. The white asterisk represents the origin of point electrical stimulation. (I and J) Patch clamp recordings of day 15+ (I) and day 39+ (J) HVPs showed typical ventricular-like action potentials. (K) Whole cell patch clamp recordings of day 21 and day 40 HVP-derived ventricular cardiomyocytes. Cultures demonstrated that there were no significant differences in various AP parameters between the two time points, suggesting that in vitro, HVPs reached maturity by day 18. (L) Representative I_f traces in the presence of 1 mM Ba²⁺. (M) Patch clamp recording comparison of I_f in ES03- and HES2-derived ventricular cardiomyocytes. Steady-state I-V (left) and steady-state activation relations (right) for I_f (n = 12). (N and O) Whole cell patch clamp recording of I_Na in ES03. (N) Representative I_Na traces during activation (left) and inactivation (right). (O) Plots of peak I_Na density I-V relationship (left) and steady-state activation/inactivation (right), n = 5. Histograms and traces are shown as mean ± SEM.