Fig. 2.
Differential [Ca2+]i dynamics at virtual electrodes induced by a monophasic S2. A: S2 polarity (anodal) and the location of stimulation electrodes in the mapped region. A double-headed arrow indicates the direction of epicardial fiber orientation. The membrane potential (Vm) map shows virtual electrode polarizations after a 60-mA, 10-ms monophasic anodal S2 given 200 ms after the last S1. The [Ca2+]i map was taken 40 ms after the S2. B: optical recordings at virtual anode and virtual cathode, respectively. Red arrows indicate 40 ms after S2. Blue arrows indicate the peak of a regenerative action potential. C: S2 polarity (cathodal) and the location of stimulation electrodes in the mapping region. The Vm map shows virtual electrode polarizations after a 60-mA, 10-ms monophasic cathodal S2 given 200 ms after the last S1. The [Ca2+]i map shows the [Ca2+]i distribution, which was taken 40 ms after the S2. D: optical recordings at virtual anode and virtual cathode, respectively. *Location of the tip of the electrode. F, fluorescence.