Evidence that channels below 1 pS cause the volume-sensitive chloride conductance in T84 cells.

The volume-activated chloride current of T84 human colonic cells was studied using the whole-cell patch clamp. The current appeared reliably with a mild osmotic gradient and in the absence of intracellular ATP. It reversed at the chloride equilibrium potential and was blocked by the chloride channel blocker DIDS. Development of the current was accompanied by an increase in the current noise variance, typical of increasing ion channel open probability. Noise variance was always well-fitted by a double Lorentzian relationship with corner frequencies at approximately 1.7 Hz and approximately 60 Hz. The increase in variance during development of the volume-sensitive current was mostly due to an increase in the high frequency component. The relationship between noise variance and membrane current was well-fitted by a relationship with a single channel conductance of approximately 0.2 pS.