FIG. 4.

Ca²⁺ signals in CPC-derived cardiomyocytes. (A) Gene expression analysis of Ca_v1.2, RYR2 and SERCA2b in differentiated CPC-derived cardiomyocytes (quantitative real-time RT-PCR). Black bars: cells in expansion medium; white and gray bars: cells in differentiation medium. (B) Linescan image of spontaneous Ca²⁺ release events in a population of fluo-3-loaded CPC-derived cardiomyocytes. Details in (a) and (b) show the linescan and line profiles of different forms of Ca²⁺ signal propagation across the respective cells. (C) Representative recordings of triggered Ca²⁺ release during electrical stimulation. Cells were field-stimulated at 0.1 Hz. Linescan and global line profile show temporally and spatially synchronized Ca²⁺ transients across the cell. (D) Detailed view of a global Ca²⁺ transient during electrical pacing. Three line profiles of different areas within one cell (a–c) are shown. Note the highly synchronized and rapid onset of Ca²⁺ release (arrow) despite the variability in peak amplitude and decay of the Ca²⁺ transient. The bars in A represent means±SD. Asterisks denote significant difference compared with expansion medium (***p<0.001).