Figure 5.

The HCN4 C terminus is necessary but not sufficient for ligand-independent relief of autoinhibition in CHO cells. Schematics and voltage dependence for HCN4–2tail and HCN2–4tail chimeric channels. In the schematic illustrations, HCN4 sequence is indicated in black, and HCN2 in blue. Thick lines indicate the CNBD. The voltage dependence of activation was determined from tail currents after 3-s hyperpolarizing steps to the indicated voltages in whole cell recordings from CHO cells expressing HCN4–2tail (A) or HCN2–4tail (B) in the absence (black) or presence (red) of 1 mM cAMP in the patch pipette.