Permeant anions contribute to voltage dependence of ClC-2 chloride channel by interacting with the protopore gate Article uri icon

abstract

  • It has been shown that the voltage (Vm) dependence of ClC Cl- channels is conferred by interaction of the protopore gate with H%2b ions. However, in this paper we present evidence which indicates that permeant Cl- ions contribute to Vm-dependent gating of the broadly distributed ClC-2 Cl- channel. The apparent open probability (PA) of ClC-2 was enhanced either by changing the [Cl-]i from 10 to 200 mm or by keeping the [Cl-]i low (10 mm) and then raising [Cl-]o from 10 to 140 mm. Additionally, these changes in [Cl-] slowed down channel closing at positive Vm suggesting that high [Cl-] increased pore occupancy thus hindering closing of the protopore gate. The identity of the permeant anion was also important since the PA(Vm) curves were nearly identical with Cl- or Br- but shifted to negative voltages in the presence of SCN- ions. In addition, gating, closing rate and reversal potential displayed anomalous mole fraction behaviour in a SCN-/Cl- mixture in agreement with the idea that pore occupancy by different permeant anions modifies the Vm dependence ClC-2 gating. Based on the ec1-ClC anion pathway, we hypothesized that opening of the protopore gate is facilitated when Cl- ions dwell in the central binding site. In contrast, when Cl- ions dwell in the external binding site they prevent the gate from closing. Finally, this Cl--dependent gating in ClC-2 channels is of physiological relevance since an increase in [Cl-]o enhances channel opening when the [Cl-]i is in the physiological range. © 2010 The Authors. Journal compilation.

publication date

  • 2010-01-01