Hyperpolarization-activated cyclic nucleotide-gated channel (HCN) (HCN)

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are specialized voltage-gated cation channels that open in response to membrane hyperpolarization rather than depolarization [UniProt P53420]. In the peripheral nervous system, these channels—particularly the HCN1 and HCN2 isoforms—are highly expressed on unmyelinated C-fibers, where they contribute to the pacemaker current (Ih) that regulates resting membrane potential and repetitive firing patterns [Emery et al., 2011, Science]. Under conditions of chronic inflammation or nerve injury, HCN channel activity is often pathologically increased, leading to the hyperexcitability of nociceptors and the subsequent development of neuropathic and inflammatory pain [Tsantoulas et al., 2016, Progress in Neurobiology]. Consequently, these channels have become significant therapeutic targets for analgesic development, as blocking the Ih current can effectively dampen overactive pain signaling [Noh et al., 2014, Journal of Pain Research]. However, because the HCN4 isoform is the primary driver of the heart's sinoatrial node activity, non-selective inhibitors like ivabradine carry risks of cardiovascular side effects such as bradycardia [Postea & Biel, 2011, Nature Reviews Drug Discovery]. Current research focuses on developing isoform-selective blockers or peripherally restricted agents to target C-fiber excitability while sparing cardiac and central nervous system functions.

Other names

HCN channelPacemaker channelIh channelIf channelHyperpolarization-activated cation channelHCN1HCN2HCN3HCN4

Inhibition of the hyperpolarization-activated current (Ih) to reduce the firing rate of action potentials in sensory neurons and cardiac pacemaker cells [Noh et al., 2014, Journal of Pain Research].