Abstract
Hyperpolarization-activated cyclic nucleotide-gated (HCN) currents are essential regulators in rhythmic generation, membrane excitability, and synaptic transmission. Four subtypes of HCN channels (HCN1-4) have been cloned so far in mammals. HCN channels form tetramers and each subunit has 6 transmembrane domains and one pore region, an architecture shared with voltage-gated potassium channels. We previously demonstrated that the first transmembrane segment (S1) and the S1-S2 loop endow different activation kinetics between HCN1 and HCN4. We investigated the structural basis of the ability of S1 to affect activation kinetics by replacing each individual S1 residue in HCN1 with a tryptophan (Trp) residue, a Trp perturbation scan. Presence or absence of current was consistent with the predicted α-helical structure of the S1 transmembrane segment. Two Trp mutations introduced in the middle of S1 prevented normal channel closure. These results suggest that S1 might interact with the mobile part of the voltage sensor (S4). Here, we introduced multiple cysteine mutations into the voltage sensor domain and investigated mutual interaction among transmembrane segments. [J Physiol Sci. 2008;58 Suppl:S71]
