Thermodynamic cycle for a hyperpolarization- and ligand-activated ion channels. In this case, our reference state is where all the gating charges are in activated conformation and all the ligand binding sites are unoccupied (at depolarizing voltages and zero ligand concentration). The choice of reference state is based on the considerations of type of coupling between voltage- and ligand-dependent pathways. The final state of the system is where all the gating charges are in the resting conformation and ligand binding sites are saturated. This state will be preferred when the voltage is low and the ligand concentration is high. As in the previous thermodynamic cycle, the net free energy of activation of this channel can be calculated by two alternate paths.