We used patch clamp techniques to identify and characterize a variety of K+ channels in primary human peripheral T lymphocytes. The most common channel observed in cell-attached configuration was voltage gated and inactivating. In ensemble averages, the kinetics of its activation and inactivation were similar to those of the whole-cell, voltage-gated K+ current described previously (Cahalan, M. D., K. G. Chandy, T. E. DeCoursey, and S. Gupta. 1985. J. Physiol. [Lond.]. 358:197-237; Deutsch, C., D. Krause, and S. C. Lee. 1986. J. Physiol. [Lond.]. 372:405-423), suggesting that this channel underlies the major portion of the outward current in lymphocytes. A small fraction of the time, this or another very similar channel was observed to inactivate significantly more slowly. Another channel type observed in cell-attached recording was seen less frequently and was transient in its appearance. This channel has a unitary conductance of approximately 10 pS, similar to the voltage-gated channel, but its voltage-independent gating, lack of inactivation, and different kinetic parameters showed it to be distinct. In whole-cell recording there is often a significant plateau current during sustained depolarization. Experiments using whole-cell and excised outside-out configurations indicate that at least part of this residual current is carried by K+ and, as opposed to the predominant voltage-gated current, is charybdotoxin insensitive. These findings are consistent with evidence that implicates charybdotoxin-sensitive and -insensitive components in T lymphocyte proliferation and volume regulation.

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