intracellularly cyclic nucleotide-activated monoatomic cation channel activity intracellularly cAMP-activated cation channel activity intracellular cAMP activated cation channel activity intracellular adenosine 3',5'-cyclophosphate activated cation channel activity molecular_function GO:0005222 HCN channel activity intracellular cAMP-activated cation channel activity Enables the transmembrane transfer of a cation by a channel that opens when intracellular cAMP has been bound by the channel complex or one of its constituent parts. intracellular 3',5'-cAMP activated cation channel activity intracellular cyclic AMP activated cation channel activity intracellular 3',5' cAMP activated cation channel activity hyperpolarization-activated cyclic nucleotide-gated channel activity