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Modulation of voltage-dependent properties of a swelling-activated Cl- current.

Voets T, Droogmans G, Nilius B - J. Gen. Physiol. (1997)

Bottom Line: The inactivation process was significantly accelerated by reducing the pH, increasing the Mg2+ concentration or reducing the Cl- concentration of the extracellular solution.Additionally, the permeant anion and the channel blockers, but not external pH or Mg2+, modulated the recovery from inactivation.In conclusion, our results show that the voltage-dependent properties of ICl,swell are strongly influenced by external pH, external divalent cations, and by the nature of the permeant anion.

View Article: PubMed Central - PubMed

Affiliation: KU Leuven, Laboratorium voor Fysiologie, Campus Gasthuisberg, B-3000 Leuven, Belgium.

ABSTRACT
We used the patch-clamp technique to study the voltage-dependent properties of the swelling-activated Cl- current (ICl,swell) in BC3H1 myoblasts. This Cl- current is outwardly rectifying and exhibits time-dependent inactivation at positive potentials (potential for half-maximal inactivation of +75 mV). Single-channel Cl- currents with similar voltage-dependent characteristics could be measured in outside-out patches pulled from swollen cells. The estimated single-channel slope conductance in the region between +60 and +140 mV was 47 pS. The time course of inactivation was well described by a double exponential function, with a voltage-independent fast time constant (approximately 60 ms) and a voltage-dependent slow time constant (>200 ms). Recovery from inactivation, which occurred over the physiological voltage range, was also well described by a double exponential function, with a voltage-dependent fast time constant (10-80 ms) and a voltage-dependent slow time constant (>100 ms). The inactivation process was significantly accelerated by reducing the pH, increasing the Mg2+ concentration or reducing the Cl- concentration of the extracellular solution. Replacing extracellular Cl- by other permeant anions shifted the inactivation curve in parallel with their relative permeabilities (SCN- > I- > NO3- > Cl- > gluconate). A leftward shift of the inactivation curve could also be induced by channel blockers. Additionally, the permeant anion and the channel blockers, but not external pH or Mg2+, modulated the recovery from inactivation. In conclusion, our results show that the voltage-dependent properties of ICl,swell are strongly influenced by external pH, external divalent cations, and by the nature of the permeant anion.

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Voltage dependence of recovery from inactivation.  (A) Voltage protocol and current traces showing the voltage dependence of recovery from inactivation. (B) Recovery during the  500-ms step to the different voltages. (C) Current traces measured  during the 500-ms step to −120, −80, and −40 mV are shown together with single exponential (solid lines) and double exponential  (dotted lines) fits. (D) Values for τfast, (○) and (•), and τslow, (⋄)  and (♦), obtained from fits to current traces as in Fig. 4 C (open  symbols) or to the data points in Fig. 3 B (filled symbols). (E) Fractional contribution of the fast component to the recovery from inactivation.
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Figure 4: Voltage dependence of recovery from inactivation. (A) Voltage protocol and current traces showing the voltage dependence of recovery from inactivation. (B) Recovery during the 500-ms step to the different voltages. (C) Current traces measured during the 500-ms step to −120, −80, and −40 mV are shown together with single exponential (solid lines) and double exponential (dotted lines) fits. (D) Values for τfast, (○) and (•), and τslow, (⋄) and (♦), obtained from fits to current traces as in Fig. 4 C (open symbols) or to the data points in Fig. 3 B (filled symbols). (E) Fractional contribution of the fast component to the recovery from inactivation.

Mentions: This voltage dependency of the current recovery was also studied with the protocol shown in Fig. 4 A. After a 1-s voltage step to 120 mV, the membrane potential was stepped to potentials between −120 and +20 mV for 500 ms, followed by a 50-ms voltage step to +120 mV. It can be clearly seen that the inward current at potentials more negative than the reversal potential for chloride (ECl = −20 mV) rapidly increases, indicating that inactivated channels reopen at these potentials. Fig. 4 B shows the fraction of the current that has recovered at the end of the 500-ms step as a function of potential. The time course of the currents at potentials (≤−40 mV was better fitted by a double than by a single exponential (Fig. 4 C). Both τslow and τfast were voltage dependent and decreased with more hyperpolarized potentials (Fig. 4 D). Similar values for τslow and τfast were obtained by fitting the data in Fig. 3 B with Eq. 1. Additionally, the relative contributions of the fast and the slow components were voltage dependent, as the contribution of the fast component increased with hyperpolarization (Fig. 4 E).


Modulation of voltage-dependent properties of a swelling-activated Cl- current.

Voets T, Droogmans G, Nilius B - J. Gen. Physiol. (1997)

Voltage dependence of recovery from inactivation.  (A) Voltage protocol and current traces showing the voltage dependence of recovery from inactivation. (B) Recovery during the  500-ms step to the different voltages. (C) Current traces measured  during the 500-ms step to −120, −80, and −40 mV are shown together with single exponential (solid lines) and double exponential  (dotted lines) fits. (D) Values for τfast, (○) and (•), and τslow, (⋄)  and (♦), obtained from fits to current traces as in Fig. 4 C (open  symbols) or to the data points in Fig. 3 B (filled symbols). (E) Fractional contribution of the fast component to the recovery from inactivation.
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Related In: Results  -  Collection

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Figure 4: Voltage dependence of recovery from inactivation. (A) Voltage protocol and current traces showing the voltage dependence of recovery from inactivation. (B) Recovery during the 500-ms step to the different voltages. (C) Current traces measured during the 500-ms step to −120, −80, and −40 mV are shown together with single exponential (solid lines) and double exponential (dotted lines) fits. (D) Values for τfast, (○) and (•), and τslow, (⋄) and (♦), obtained from fits to current traces as in Fig. 4 C (open symbols) or to the data points in Fig. 3 B (filled symbols). (E) Fractional contribution of the fast component to the recovery from inactivation.
Mentions: This voltage dependency of the current recovery was also studied with the protocol shown in Fig. 4 A. After a 1-s voltage step to 120 mV, the membrane potential was stepped to potentials between −120 and +20 mV for 500 ms, followed by a 50-ms voltage step to +120 mV. It can be clearly seen that the inward current at potentials more negative than the reversal potential for chloride (ECl = −20 mV) rapidly increases, indicating that inactivated channels reopen at these potentials. Fig. 4 B shows the fraction of the current that has recovered at the end of the 500-ms step as a function of potential. The time course of the currents at potentials (≤−40 mV was better fitted by a double than by a single exponential (Fig. 4 C). Both τslow and τfast were voltage dependent and decreased with more hyperpolarized potentials (Fig. 4 D). Similar values for τslow and τfast were obtained by fitting the data in Fig. 3 B with Eq. 1. Additionally, the relative contributions of the fast and the slow components were voltage dependent, as the contribution of the fast component increased with hyperpolarization (Fig. 4 E).

Bottom Line: The inactivation process was significantly accelerated by reducing the pH, increasing the Mg2+ concentration or reducing the Cl- concentration of the extracellular solution.Additionally, the permeant anion and the channel blockers, but not external pH or Mg2+, modulated the recovery from inactivation.In conclusion, our results show that the voltage-dependent properties of ICl,swell are strongly influenced by external pH, external divalent cations, and by the nature of the permeant anion.

View Article: PubMed Central - PubMed

Affiliation: KU Leuven, Laboratorium voor Fysiologie, Campus Gasthuisberg, B-3000 Leuven, Belgium.

ABSTRACT
We used the patch-clamp technique to study the voltage-dependent properties of the swelling-activated Cl- current (ICl,swell) in BC3H1 myoblasts. This Cl- current is outwardly rectifying and exhibits time-dependent inactivation at positive potentials (potential for half-maximal inactivation of +75 mV). Single-channel Cl- currents with similar voltage-dependent characteristics could be measured in outside-out patches pulled from swollen cells. The estimated single-channel slope conductance in the region between +60 and +140 mV was 47 pS. The time course of inactivation was well described by a double exponential function, with a voltage-independent fast time constant (approximately 60 ms) and a voltage-dependent slow time constant (>200 ms). Recovery from inactivation, which occurred over the physiological voltage range, was also well described by a double exponential function, with a voltage-dependent fast time constant (10-80 ms) and a voltage-dependent slow time constant (>100 ms). The inactivation process was significantly accelerated by reducing the pH, increasing the Mg2+ concentration or reducing the Cl- concentration of the extracellular solution. Replacing extracellular Cl- by other permeant anions shifted the inactivation curve in parallel with their relative permeabilities (SCN- > I- > NO3- > Cl- > gluconate). A leftward shift of the inactivation curve could also be induced by channel blockers. Additionally, the permeant anion and the channel blockers, but not external pH or Mg2+, modulated the recovery from inactivation. In conclusion, our results show that the voltage-dependent properties of ICl,swell are strongly influenced by external pH, external divalent cations, and by the nature of the permeant anion.

Show MeSH
Related in: MedlinePlus