Outwardly rectifying Cl- channels in cultured human Jurkat T-lymphocytes were activated by excising a patch of membrane using the inside-out (i/o) patch-clamp configuration and holding at depolarized voltages for prolonged periods of time (1-6 min at +80 mV, 20 degrees C). The single-channel current at +80 mV was 4.5 +/- 0.3 pA and at -80 mV, it was 1.0 +/- 0.4 pA. After activation, the probability of being open (Po) for the lymphocyte channel was voltage independent. Activation of the Cl- channel in lymphocytes was temperature dependent. Nineteen percent of i/o recordings from lymphocytes made at 20 degrees C exhibited Cl- channel activity. In contrast, 49% of recordings made at 30 degrees C showed channel activity. The number of channels in an active patch was not significantly different at the two temperatures. Channel activation in excised, depolarized patches also occurred 20-fold faster at 30 degrees C than at 20 degrees C. There was no marked change in the single-channel conductance at 30 degrees C. Open-channel conductance was blocked by 200 microM indanyloxyacetic acid (IAA) or 1 mM SITS when applied to the intracellular side of the patch. The characteristics of this channel are similar to epithelial outwardly rectifying Cl- channels thought to be involved in fluid secretion.