Abstract
Cyclic nucleotide-gated (CNG) channels are directly activated by the binding of cGMP and/or cAMP, which are controlled by G-protein enzyme cascades. Their cousins, the hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels, are voltage-gated, but their voltage sensitivity is regulated by the binding of cAMP. Both CNG and HCN channels are members of the superfamily of voltage-gated cation channels. CNG channels have established roles in sensory transduction, but they are also found in many non-sensory tissues. HCN channels are best known for their pacemaking role in the cardiac sinoatrial node. Both CNG and HCN channels are excitatory, since their opening allows Na + and Ca 2+ entry. In the brain, both CNG and HCN channels are implicated in synaptic plasticity and other excitation processes, in addition to their pacemaking role in rhythmic neurons. There continues to be fast-moving research on these channels in the areas of structure/function, physiological roles, modulation, gating, permeation and development of pharmacological tools.
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