EVIDENCE THAT CHANNELS BELOW 1 PS CAUSE THE VOLUME-SENSITIVE CHLORIDECONDUCTANCE IN T84 CELLS

The volume-activated chloride current of T84 human colonic cells was s tudied 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 acco mpanied by an increase in the current noise variance, typical of incre asing ion channel open probability. Noise variance was always well-fit ted by a double Lorentzian relationship with corner frequencies at sim ilar to 1.7 Hz and similar to 60 Hz. The increase in variance during d evelopment of the volume-sensitive current was mostly due to an increa se in the high frequency component. The relationship between noise var iance and membrane current was well-fitted by a relationship with a si ngle channel conductance of similar to 0.2 pS.