Papers of the Week

HCN ion channels conducting the I current control the frequency of firing in peripheral sensory neurons signalling pain Previous studies have demonstrated a major role for the HCN2 subunit in chronic pain but a potential involvement of HCN3 in pain has not been investigated HCN3 was found to be widely expressed in all classes of sensory neurons (small, medium, large) where it contributes to I HCN3 deletion increased the firing rate of medium, but not small, sensory neurons Pain sensitivity both acutely and following neuropathic injury was largely unaffected by HCN3 deletion, with the exception of a small decrease of mechanical hyperalgesia in response to a pinprick We conclude that HCN3 plays little role in either acute or chronic pain sensation HCN ion channels generate an inward current that can regulate action potential firing in somatosensory nerve fibres and can play an important role in pain sensation. The HCN1 isoform plays a limited role only in cold sensation following nerve injury. HCN2, on the other hand, is a key regulator of excitability in nociceptive nerve fibres, and controls the perception of inflammatory and neuropathic pain, but has no influence on acute pain sensation. Here we examine a potential role for the HCN3 isoform in neuronal excitability and pain. HCN3 is widely expressed in somatosensory neurons, and contributes to the regulation of firing of action potentials in medium-sized neurons, amongst which many have a nociceptive function. Genetic deletion of HCN3, however, had little impact on acute pain sensation, on inflammatory pain, nor on pain following nerve injury (neuropathic pain). We conclude that HCN3 does not play an important role in pain sensation.