Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are key modulators of neuronal activity by providing the depolarizing cation current Ih involved in rhythmogenesis, dendritic integration and synaptic transmission. These tasks critically depend on the availability of the channels which can be dynamically regulated by intracellular cAMP. Using affinity purification and high-resolution mass spectrometry we show that HCN channels in the mammalian brain may be co-assembled with the PEX5R/Trip8b protein that is identified as an exclusive ß-subunit of HCN channels. Co-assembly of PEX5R/Trip8b affects HCN channel gating in a subtype-dependent and mode-specific way: activation of HCN2 and HCN4 by cAMP is largely impaired, while gating by phosphoinositides and basal voltage-dependence remain unaffected. De novo expression of PEX5R/Trip8b in cardiomyocytes abolishes ß-adrenergic stimulation of HCN channels. These results demonstrate that PEX5R/Trip8b is an intrinsic auxiliary subunit of brain HCN channels and establish HCN-PEX5R/Trip8b co-assembly as a novel mechanism to control the channels responsiveness to cyclic nucleotide signaling.

This work was supported by the grant KL1168/6 of the DFG to N.K.