Permeant anions contribute to voltage dependence of ClC-2 chloride channel by interacting with the protopore gate.
It has been shown that the voltage (V(m)) dependence of ClC Cl(-) channels is conferred by interaction of the protopore gate with H(+) ions. However, in this paper we present evidence which indicates that permeant Cl(-) ions contribute to V(m)-dependent gating of the broadly distributed ClC-2 Cl() channel. The apparent open probability (P(A)) 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 V(m) 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 P(A)(V(m)) 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 V(m) 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.
Sánchez-Rodríguez
Jorge E
JE
Instituto de Física, Universidad Autónoma de San Luis Potosí, Av. Dr Manuel Nava no. 6, Zona Universitaria, San Luis Potosí, SLP 78290, México.
De Santiago-Castillo
José A
JA
Arreola
Jorge
J
D000818:Animals; D000090007:CLC-2 Chloride Channels; D002478:Cells, Cultured; D018118:Chloride Channels / Q000502:physiology*; D002712:Chlorides / Q000378:metabolism / Q000502:physiology*; D015640:Ion Channel Gating / Q000502:physiology*; D051379:Mice; D010306:Parotid Gland / Q000502:physiology; D013861:Thiocyanates / Q000494:pharmacology
D000090007:CLC-2 Chloride Channels; D018118:Chloride Channels; D002712:Chlorides; D013861:Thiocyanates; C031760:thiocyanate