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Different fast-gate regulation by external Cl(-) and H(+) of the muscle-type ClC chloride channels.

Chen MF, Chen TY - J. Gen. Physiol. (2001)

Bottom Line: Varying the external Cl(-) concentrations ([Cl(-)](o)) shifts the P(o)-V curve in parallel along the voltage axis, whereas reducing external pH mainly increases the minimal P(o) of the curve.Thus, the H(+) effect on the fast gating appears not to be a consequence of an increase in the Cl(-) binding affinity.We previously found that a hyperpolarization-favored opening process is important to determine the fast-gate P(o) of ClC-0 at very negative voltages.

View Article: PubMed Central - PubMed

Affiliation: Center for Neuroscience, University of California, Davis, CA 95616, USA.

ABSTRACT
The fast gate of the muscle-type ClC channels (ClC-0 and ClC-1) opens in response to the change of membrane potential (V). This gating process is intimately associated with the binding of external Cl(-) to the channel pore in a way that the occupancy of Cl(-) on the binding site increases the channel's open probability (P(o)). External H(+) also enhances the fast-gate opening in these channels, prompting a hypothesis that protonation of the binding site may increase the Cl(-) binding affinity, and this is possibly the underlying mechanism for the H(+) modulation. However, Cl(-) and H(+), modulate the fast-gate P(o)-V curve in different ways. Varying the external Cl(-) concentrations ([Cl(-)](o)) shifts the P(o)-V curve in parallel along the voltage axis, whereas reducing external pH mainly increases the minimal P(o) of the curve. Furthermore, H(+) modulations at saturating and nonsaturating [Cl(-)](o) are similar. Thus, the H(+) effect on the fast gating appears not to be a consequence of an increase in the Cl(-) binding affinity. We previously found that a hyperpolarization-favored opening process is important to determine the fast-gate P(o) of ClC-0 at very negative voltages. This [Cl(-)](o)-independent mechanism attracted little attention, but it appears to be the opening process that is modulated by external H(+).

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Quasi steady-state inactivation curves of the WT ClC-0 and the C212S mutant at different pH values. (A) Whole oocyte currents of the WT and C212S at three external pH. See materials and methods for the voltage protocol to examine the slow-gate inactivation. Dotted lines represent zero-current level. (B) Quasi steady-state inactivation curve of the WT (left, n = 3) and the C212S mutant (right, n = 4) at pH 7.6 (circles), 9.6 (triangles), and 5.6 (squares).
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Figure 1: Quasi steady-state inactivation curves of the WT ClC-0 and the C212S mutant at different pH values. (A) Whole oocyte currents of the WT and C212S at three external pH. See materials and methods for the voltage protocol to examine the slow-gate inactivation. Dotted lines represent zero-current level. (B) Quasi steady-state inactivation curve of the WT (left, n = 3) and the C212S mutant (right, n = 4) at pH 7.6 (circles), 9.6 (triangles), and 5.6 (squares).

Mentions: To examine the quasi steady-state inactivation curve of the channel (see Fig. 1), a protocol modified from a previously described method (Pusch et al. 1997; Chen 1998) was used. The membrane potential (V) was held at −30 mV, and a 3.5-s prepulse from 0 to −140 mV in −10-mV steps was followed by a 0.4-s test pulse at +60 mV. The current was measured at the end of the +60-mV test pulse, and was normalized to the maximal current obtained at pH 7.6.


Different fast-gate regulation by external Cl(-) and H(+) of the muscle-type ClC chloride channels.

Chen MF, Chen TY - J. Gen. Physiol. (2001)

Quasi steady-state inactivation curves of the WT ClC-0 and the C212S mutant at different pH values. (A) Whole oocyte currents of the WT and C212S at three external pH. See materials and methods for the voltage protocol to examine the slow-gate inactivation. Dotted lines represent zero-current level. (B) Quasi steady-state inactivation curve of the WT (left, n = 3) and the C212S mutant (right, n = 4) at pH 7.6 (circles), 9.6 (triangles), and 5.6 (squares).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2233746&req=5

Figure 1: Quasi steady-state inactivation curves of the WT ClC-0 and the C212S mutant at different pH values. (A) Whole oocyte currents of the WT and C212S at three external pH. See materials and methods for the voltage protocol to examine the slow-gate inactivation. Dotted lines represent zero-current level. (B) Quasi steady-state inactivation curve of the WT (left, n = 3) and the C212S mutant (right, n = 4) at pH 7.6 (circles), 9.6 (triangles), and 5.6 (squares).
Mentions: To examine the quasi steady-state inactivation curve of the channel (see Fig. 1), a protocol modified from a previously described method (Pusch et al. 1997; Chen 1998) was used. The membrane potential (V) was held at −30 mV, and a 3.5-s prepulse from 0 to −140 mV in −10-mV steps was followed by a 0.4-s test pulse at +60 mV. The current was measured at the end of the +60-mV test pulse, and was normalized to the maximal current obtained at pH 7.6.

Bottom Line: Varying the external Cl(-) concentrations ([Cl(-)](o)) shifts the P(o)-V curve in parallel along the voltage axis, whereas reducing external pH mainly increases the minimal P(o) of the curve.Thus, the H(+) effect on the fast gating appears not to be a consequence of an increase in the Cl(-) binding affinity.We previously found that a hyperpolarization-favored opening process is important to determine the fast-gate P(o) of ClC-0 at very negative voltages.

View Article: PubMed Central - PubMed

Affiliation: Center for Neuroscience, University of California, Davis, CA 95616, USA.

ABSTRACT
The fast gate of the muscle-type ClC channels (ClC-0 and ClC-1) opens in response to the change of membrane potential (V). This gating process is intimately associated with the binding of external Cl(-) to the channel pore in a way that the occupancy of Cl(-) on the binding site increases the channel's open probability (P(o)). External H(+) also enhances the fast-gate opening in these channels, prompting a hypothesis that protonation of the binding site may increase the Cl(-) binding affinity, and this is possibly the underlying mechanism for the H(+) modulation. However, Cl(-) and H(+), modulate the fast-gate P(o)-V curve in different ways. Varying the external Cl(-) concentrations ([Cl(-)](o)) shifts the P(o)-V curve in parallel along the voltage axis, whereas reducing external pH mainly increases the minimal P(o) of the curve. Furthermore, H(+) modulations at saturating and nonsaturating [Cl(-)](o) are similar. Thus, the H(+) effect on the fast gating appears not to be a consequence of an increase in the Cl(-) binding affinity. We previously found that a hyperpolarization-favored opening process is important to determine the fast-gate P(o) of ClC-0 at very negative voltages. This [Cl(-)](o)-independent mechanism attracted little attention, but it appears to be the opening process that is modulated by external H(+).

Show MeSH