Figure 1: Depiction of HCN4 pore region with the channel inhibitor ivabradine below the K⁺-occupied selectivity filter (SF). The protein is depicted as gray cartoon, with carbonyl oxgens within the selectivity filter shown in the stick repre- sentation. A violet sphere represents the K⁺ cation in the lower SF, while ivabradine is depicted in the pore below in the ball-and-stick representation (with the nitrogen atom in the functionally relevant tertiary ammonium group colored in blue). Only two opposing monomers of the tetrameric channel are shown for visual clarity.