MODULATION BY EXTRACELLULAR AND INTRACELLULAR IODIDE OF VOLUME-ACTIVATED CL- CURRENT IN HELA-CELLS

The patch-clamp technique was used to study the effect of extracellula r and intracellular iodide on the properties of the volume-activated a nion current in HeLa cells. Upon hypotonic challenge, HeLa cells respo nded by activating an outwardly rectifying Cl- current. Replacement of extracellular Cl- by I-, a more permeable anion, increased the peak o utward and inward current, reduced the magnitude of deactivation obser ved at depolarized potentials and shifted the half-maximal (V-0.5) dea ctivation voltage towards more positive values. On the other hand, whe n internal Cl- was replaced by I- the volume-activated current was not observed in normal, Cl--rich hypotonic extracellular solution. Howeve r, switching to a hypotonic extracellular solution containing a mixtur e of Cl- and I- resulted in the activation of the volume-sensitive cur rent. Furthermore, once the current was activated, I- could be exclude d from the external solution without significantly affecting the curre nt properties These results suggest that the permeant anion plays a cr ucial role in the gating mechanism of the volume-activated Cl- current , influencing the swelling-dependent activation and the voltage-depend ent deactivation processes.