Fig. 4.
Δ[Ca2+]i amplitudes between virtual anodes and virtual cathodes at different S1-S2 coupling intervals. A: Δ[Ca2+]i amplitude (net increase in [Ca2+]i by S2 stimulation compared with 7th S1-paced beat) at virtual anode and virtual cathode when S2 was monophasic anodal. The Δ[Ca2+]i amplitudes progressively and significantly increased with increasing coupling interval. B: Δ[Ca2+]i amplitude at virtual anode (white bars) and virtual cathode (black bars) induced by monophasic cathodal S2. *P < 0.01 when compared with Δ[Ca2+]i amplitude at virtual cathode. #P < 0.01 and †P < 0.01 when compared with Δ[Ca2+]i amplitude of virtual anode and virtual cathode, respectively, at the S1-S2 coupling interval of 150 ms.