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Current
From KU Leuven, Laboratorium voor Fysiologie, Campus Gasthuisberg, B-3000 Leuven, Belgium
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 (~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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