Effect of SPX on <i>I</i>_CaL and AP in adult mouse cardiac myocytes.

<p>A, Representative traces of <i>I</i>_CaL during a 200-ms voltage-clamp pulse from −40 to 0 mV before (black) and after (red) exposure to 300 μM SPX. B–C, current–voltage (<i>I</i>-V) relationships of <i>I</i>_peak (■, B) and <i>I</i>_{end of pulse} (●, C) under control conditions (black) and after application of 300 μM SPX (red) (n = 4). D. SPX prolonged APs of adult mouse cardiomyocyte at a stimulation rate of 2 Hz. E, Plot of APD₉₀ over a range of stimulation rate in adult mouse cardiomyocytes in the absence and presence of SPX. F. Example of AP recorded after 30 min exposure to SPX at a slow stimulation rate (0.1 Hz). EADs (arrows) and delayed afterdepolarization (DAD; d) were observed, G. Summary data showing frequency of afterdepolarizations in control and SPX-treated cells. Incidence of EAD or DAD was analyzed using Fisher's exact test. *<i>P</i> < 0.05, **<i>P</i> < 0.01.