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Department of Physiology, University of Pennsylvania, Philadelphia 19104-6085.

1. Using whole-cell patch-clamp techniques, we found that the voltage-dependent K+ conductance in human peripheral blood T lymphocytes is enhanced threefold at alkaline intracellular pH (pHi) compared to acid pHi. This pH dependence can be described by a model having two strongly co-operative proton binding sites with pka 7.15. A similar pHi sensitivity exists for K+ conductance in mitogen-activated cells. 2. The reversal potential, threshold voltage for activation of the K+ conductance, and voltage dependence of steady-state inactivation are not affected by pHi. Activation and inactivation kinetics are also unchanged. 3. Single-channel measurements made in whole-cell patch-clamp mode indicate that the effect of intracellular pH on the amplitudes of single-channel events parallels, but does not wholly account for, the effect of pHi on the macroscopic currents. 4. Lowering extracellular pH (pHo) shifts the threshold for activation of the K+ current to a more depolarized voltage, consistent with a surface charge screening effect. Apparent changes in peak current and activation kinetics at acid pHo can be accounted for by this voltage shift. An additional slowing of inactivation kinetics at low pHo does occur. 5. The relevance of the pH sensitivity of the voltage-gated K+ conductance to lymphocyte mitogenesis and volume regulation is discussed.

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