Gating currents from a Kv3 subfamily potassium channel: charge movement and modification by BDS-II toxin.
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 approximately 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((1/2))) 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((1/2)) of Q(off) of -80.9 +/- 0.8 mV (n = 3), which allowed approximately 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.
Wang
Zhuren
Z
Department of Anaesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, BC, Canada.
Robertson
Brian
B
Fedida
David
D
D000818:Animals; D002478:Cells, Cultured; D003064:Cnidarian Venoms / Q000494:pharmacology*; D004594:Electrophysiology; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects*; D007700:Kinetics; D009865:Oocytes; D051381:Rats; D051670:Shaw Potassium Channels / Q000378:metabolism*; D014982:Xenopus laevis
C072544:BDS II protein, Anemonia sulcata; D003064:Cnidarian Venoms; C489595:Kcnc2 protein, rat; D051670:Shaw Potassium Channels