Figure 4.

Properties of HCN blockade. Histograms show current values measured in the presence of compounds (used at concentrations around EC₅₀ obtained for each HCN isoform), measured at the first (1st) and the 30th step after restoring hyperpolarization, following a 2 min pulse at −30 mV (see text and voltage protocol at the top). Values were normalized with respect to the pre-drug value (dotted line). (A) mHCN1; (B) hHCN4. (C and D) Examples of the current at −120 mV recorded in HCN1 (C) and in HCN4 (D) during the experiment time course (indicated at the top of figure) in the presence of 7 µM EC32. The dotted lines indicate the current values during the activation of the channel in the presence of EC32 before the period at −30 mV and immediately after resuming stimulation. In the case of mHCN1 (C), the difference between the dotted lines represents the ‘closed channel’ blockade; as for hHCN4 (D), the lack of difference between the levels indicates that channel blockade occurs only after stimulation was resumed. n= 4, *P < 0.05, **P < 0.01; §P < 0.001; †P < 0.0001 versus CTR.