HCN channels generate hyperpolarization-activated cation currents (Ih) that are involved in pacemaking activity in heart and brain. For still enigmatic reasons, their voltage range of activation varies widely across cell types. Moreover, voltage dependence of channel activation shifts to more hyperpolarized potentials by 40-50 mV in excised patches or prolonged whole-cell recordings; this shift is only partially antagonized by saturating concentrations of cAMP.

Here, we show that membrane phospholipids such as phosphatidylinositol-4,5-bisphosphate (PIP2) activate HCN channels by shifting their voltage-dependent activation to more depolarized potentials by as much as 20 mV. This shift is independent of cyclic nucleotides and occurs in both WT and mutant HCNs that lack activation by cAMP. When applied to extensively perfused membrane patches the combined action of PIP2 and cAMP restores voltage-dependent activation of HCN channels as observed prior to patch excision. These results demonstrate gating of HCN channels by PIP2 and suggest phospholipids as a potent tool to modulate excitability in neurons and cardio-myocytes.