The function of HCN1 (hyperpolarization activated cyclic nucleotide gated potassium channel 1, Ensembl gene identifier ENSG00000164588) is as follows. Hyperpolarization-activated ion channel that are permeable to sodium and potassium ions (PubMed:15351778, PubMed:28086084). Displays lower selectivity for K(+) over Na(+) ions (PubMed:28086084). Contributes to the native pacemaker currents in heart (If) and in the generation of the I(h) current which controls neuron excitability (PubMed:29936235, PubMed:30351409). Participates in cerebellar mechanisms of motor learning (By similarity). May mediate responses to sour stimuli (By similarity). {ECO:0000250|UniProtKB:O88704, ECO:0000269|PubMed:15351778, ECO:0000269|PubMed:28086084, ECO:0000269|PubMed:29936235, ECO:0000269|PubMed:30351409}.