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Conserved Voltage Sensor

The voltage sensor for the depolarization-activated, Shaker K+ channel (Kv) is well characterized as the transmembrane segment S4. In Kv channels, depolarization stimulates the outward movement (more residues of S4 exposed to the extracellular surface), and the channel opens. Männikkö et al. report that hyperpolarization-activated, cyclic nucleotide-gated, cation nonselective channels (HCN) also use movement of the S4 domain to control channel gating. Cysteine accessibility studies on channels expressed in Xenopus oocytes were used to show that outward movement of the S4 domain was associated with closure of HCN channels at depolarized membrane potentials. Thus, depolarization- and hyperpolarization-activated channels use a similar voltage-sensing mechanism. However, outward movement of S4 results in channel closure for the hyperpolarization-activated HCN channel and channel opening for the depolarization-activated Kv channels. In this way, opposite changes in membrane potential can act through the same domain to produce channel activation. R. Männikkö, F. Elinder, H. P. Larsson, Voltage-sensing mechanism is conserved among ion channels gated by opposite voltages. Nature 419, 837-841 (2002). [Online Journal]