Which of the following is the function of Hyperpolarizing Cyclic Nucleotide (HCN) gated channels?
Cardiac rhythm generation
Generation of mitochondrial action potential
Myocardial muscle contraction
Memory formation
Ans: A. Cardiac rhythm generationHyperpolarizing Cycling Nucleotide (HCN) gated channels:Present in SA & AV nodes.Channel opens in hyperpolarization phase.Essential for generating pacemaker potential in SA Node (cardiac rhythm generation).HCN-Nervous systemHCN-Cardiovascular systemControls neuronal excitability, synaptic transmission & rhythmic oscillatory activity in individual neurons & neuronal networks.Play an impoant role in synaptic plasticity & memory, thalamocoical rhythms & somatic sensation.Some evidence indicates they also play a role in mechanisms of epilepsy & pain.HCN4 is the main isoform expressed in the SA node, but low levels of HCN1 & HCN2 are also seen.Current through HCN channels, called "funny current or pacemaker current", plays a key role in generation & modulation of cardiac rhythmicity.