Hyperpolarization-activated cyclic nucleotide-gated channel 1-4 (HCN1-4)

Hyperpolarization-activated cyclic nucleotide-gated (HCN1-4) channels are a family of four voltage-gated cation channels that are uniquely activated by membrane hyperpolarization and modulated by intracellular cyclic nucleotides like cAMP [1, 2]. Often referred to as pacemaker channels, they generate the If (funny) current in the heart's sinoatrial node and the Ih current in neurons, which are essential for rhythmic electrical activity and maintaining resting membrane potential [8, 13]. In the cardiovascular system, HCN4 is the dominant isoform responsible for setting the heart rate, making it a primary target for drugs like ivabradine used in heart failure and stable angina [4, 8]. In the nervous system, HCN1 and HCN2 are widely expressed and regulate neuronal excitability, dendritic integration, and pain signaling [3, 10]. Dysregulation of these channels is linked to conditions such as epilepsy, neuropathic pain, and cardiac arrhythmias [4, 13]. Therapeutic strategies involve blocking these channels to reduce heart rate or neuronal over-excitability, though isoform selectivity remains a challenge to avoid off-target effects like visual disturbances (phosphenes) or unwanted CNS impacts [12, 14]. Recent research also explores their role in depression and Parkinson's disease, highlighting their broad potential as therapeutic targets [6, 7].

Other names

HCN channelsPacemaker channelsFunny current channelsIh channelsIq channelsBCNG channelsHyperpolarization-activated cation channels

Inhibition of the hyperpolarization-activated current (Ih or If) by binding to the channel pore or voltage-sensing domain, thereby reducing the rate of diastolic depolarization in the heart or decreasing neuronal excitability [1, 12, 14].