Block of murine HCN1, HCN2 and HCN212 channels by IVB. Time-course of normalized IHCN1 (A, right), IHCN2 (B, right) and IHCN212 (C, right) current amplitude. We used a voltage protocol in which activating/deactivating steps (−100/+5 mV, every 6 s) were applied from a holding potential of −35 mV for tens of seconds. Then, at the time of IVB (3 μM) application membrane voltage was held at −35 mV for 90 s. At this voltage the HCN channels are closed. Then, in the continuous presence of IVB, the pulsing protocol was resumed. Sample normalized current traces recorded at the times indicated are shown on the left side of each panel. D. Mean percentage steady-state block of human HCN4, and murine HCN2, HCN1 and HCN212 currents induced by IVB 3 μM (n=4–6). Values reported for HCN4 current (gray bar) are taken from.13 *P<0.05 vs. HCN4 and HCN2.