Modulation by extracellular and intracellular iodide of volume-activated Cl - current in HeLa cells

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Abstract
The patch-clamp technique was used to study the effect of extracellular and intracellular iodide on the properties of the volume-activated anion current in HeLa cells. Upon hypotonic challenge, HeLa cells responded by activating an outwardly rectifying Cl– current. Replacement of extracellular Cl– by I–, a more permeable anion, increased the peak outward and inward current, reduced the magnitude of deactivation observed at depolarized potentials and shifted the half-maximal (V0.5) deactivation voltage towards more positive values. On the other hand, when internal Cl– was replaced by I– the volume-activated current was not observed in normal, Cl–-rich hypotonic extracellular solution. However, switching to a hypotonic extracellular solution containing a mixture of Cl– and I– resulted in the activation of the volume-sensitive current. Furthermore, once the current was activated, I– could be excluded from the external solution without significantly affecting the current properties. These results suggest that the permeant anion plays a crucial role in the gating mechanism of the volume-activated Cl– current, influencing the swelling-dependent activation and the voltage-dependent deactivation processes.

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