Which of the following is the function of Hyperpolarizing Cyclic Nucleotide (HCN) gated channels?
(A) Cardiac rhythm generation (B) Generation of mitochondrial action potential (C) Myocardial muscle contraction (D) Memory formation
(A) 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.