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Gating currents from a Kv3 subfamily potassium channel: charge movement and modification by BDS‐II toxin
Author(s) -
Wang Zhuren,
Robertson Brian,
Fedida David
Publication year - 2007
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2007.140145
Subject(s) - gating , chemistry , shaker , time constant , potassium channel , biophysics , electrophysiology , herg , amplitude , ion channel , analytical chemistry (journal) , physics , neuroscience , electrical engineering , biochemistry , optics , engineering , chromatography , quantum mechanics , vibration , biology , receptor
Kv3 channels have a major role in determining neuronal excitability, and are characterized by ultra‐rapid kinetics of gating and a high activation threshold. However, the gating currents, which occur as a result of positional changes of the charged elements in the channel structure during activation, are not well understood. Here we report a study of gating currents from wild‐type Kv3.2b channels, expressed in human embryonic kidney (HEK) cells to facilitate high time‐resolution recording. On‐gating currents ( I g,on ) had extremely rapid kinetics such that at +80 mV, the time constant for the decay of I g,on was only ∼0.3 ms. Decay of I g,on appeared mono‐exponential at all potentials studied, and in support of this, the charge–voltage ( Q–V ) relationship was fitted with a single Boltzmann function, supporting the idea that only one charge system is required to account for the time course of I g,on and the voltage dependence of Q on . The voltage ( V ½ ) for half movement of gating charge was −8.4 ± 4.0 mV ( n = 6), which closely matches the voltage dependence of activation of Kv3.2b ionic currents reported before. Depolarizations to more positive potentials than 0 mV decreased the amplitude and slowed the decay of the off‐gating currents ( I g,off ), suggesting that a rate‐limiting step in opening was present in Kv3 channels as in Shaker and other Kv channels. Return of charge was negatively shifted along the potential axis with a V ½ of Q off of −80.9 ± 0.8 mV ( n = 3), which allowed ∼90% charge return upon repolarization to −100 mV. BDS‐II toxin apparently reduced I g,on , and greatly slowed the kinetics of I g,on , while shifting the Q–V relationship in the depolarizing direction. However, the Q–V relationship remained well fitted by a single Boltzmann function. These data provide the first description of Kv3 gating currents and give further insight into the interaction of BDS toxins and Kv3 channels.