Nifedipine reduced spontaneous Ca²⁺ transient activity in ES cell-derived CMs.

<p>(<b><i>A</i></b>) Representative tracings of spontaneous Ca²⁺ transients recorded in spontaneously beating CMs from control and nifedipine-treated cultures. Fluorescence images (labeled with Fura 2 AM) of the recorded cells are shown on the left panel. (<b><i>B</i></b>) Left, spontaneous Ca²⁺ transients recorded from CMs derived under untreated (top) and nifedipine-treated (bottom) condition before and after caffeine application. Right, caffeine-induced peak amplitude (top, right) of the Ca²⁺ signals and Fractional release (bottom, right) calculated as the ratio of peak Ca²⁺ concentration under control condition to peak Ca²⁺ concentration induced by caffeine. (<b><i>C–F</i></b>) Comparison of the frequency (<i>C</i>), amplitude (<i>D</i>), maximum upstroke (<i>E</i>) and decay (<i>F</i>) velocity of spontaneous Ca²⁺ transients on day 12 in controls (<i>n</i> = 10) and nifedipine-treated <i>(n</i> = 8) cultures.