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Department of Physiology, University of Toronto, Ontario, Canada.

1. A voltage-dependent K+ channel called the 'n' type (for 'normal') is the most prevalent ion channel found in whole-cell recordings from T lymphocytes. In whole-cell patch-clamp recordings activity of the n-type channel is affected by mitogenic agents, pH, Ca2+ and temperature but not by cyclic nucleotides. Because channel properties and regulation can depend on cytoplasmic components we sought to reassess the properties of K+ channels in intact, normal human T lymphocytes using cell-attached, patch-clamp recordings. In the present study, we show that the predominant K+ channel in resting, intact cells is the n type and is affected by voltage, temperature and Ca2+ in ways similar to the disrupted cell. Moreover, K+ channels are activated by agents that raise cyclic AMP in intact cells. 2. In cell-attached recordings, we found voltage-activated K+ channels in about 60% of patches at room temperature. The channel was K+ selective as judged from the reversal potential under different Ka(+)-K+ gradients and at different resting membrane potentials. Some patches were subsequently excised and the selectivity further confirmed. The current-voltage relation was inwardly rectifying under symmetrical K+ concentrations and had a slope conductance of 9.4 pS at 50 mV depolarized and 23.8 pS at 50 mV hyperpolarized from the resting potential. From the reversal potentials under various conditions the cell resting potential was -51 +/- 1 mV in normal NaCl saline and about 0 mV when the bath contained 150 mM-KCl saline. Two other types of K+ channel were seen in resting, intact cells, but were much less common (less than 5% and 11% of patches). A large-conductance K+ channel was seen in less than 1% of inside-out patches. 3. The predominant K+ channel in intact, resting T lymphocytes was confirmed as the n type underlying the whole-cell K+ current evoked by voltage steps. In cell-attached patches there was a low, steady-state level of activity at the resting potential but activity was greatly increased by depolarizing voltage jumps. Steady-state inactivation could be removed by a hyperpolarizing pre-pulse. Ensemble currents constructed by summing channel openings during repeated voltage jumps showed sigmoid kinetics of current activation and a monoexponential decay phase. These kinetics were well fitted by a Hodgkin-Huxley-type n4j kinetic model with time constants very similar to the whole-cell current of disrupted cells. Moreover, the kinetics depended on the external K+ concentration as previous research has shown.(ABSTRACT TRUNCATED AT 400 WORDS)

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