Modulation of Voltage-dependent Properties of a Swelling-activated Cl− Current

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.