Microelectrode ion flux estimation (MIFE) and patch-clamp techniques were combined for noninvasive K+ flux measurements and recording of activities of the dominant K+ channels in the early phases of apoptosis in Jurkat cells. Staurosporine (STS, 1 μM) evoked rapid (peaking around 15 min) transient K+ efflux, which then gradually decreased. This transient K+ efflux occurred concurrently with the transient increase of the K+ background (Kbg) TWIK-related spinal cord K+ channel-like current density, followed by a drastic decrease and concomitant membrane depolarization. The Kv1.3 current density remained almost constant. Kv1.3 activation was not altered by STS, whereas the inactivation was shifted to more positive potentials. Contribution of Kbg and Kv1.3 channels to the transient and posttransient STS-induced K+ efflux components, respectively, was confirmed by the effects of bupivacaine, predominantly blocking Kbg current, and the Kv1.3-specific blocker margatoxin. Channel-mediated K+ efflux provoked a substantial cellular shrinkage and affected the activation of caspases.

In this study, we present patch-clamp characterization of the background potassium current in human lymphoma (Jurkat cells), generated by voltage-independent 16 pS channels with a high ( approximately 100-fold) K+/Na+ selectivity. Depending on the background K+ channels density, from few per cell up to approximately 1 open channel per microm2, resting membrane potential was in the range of -40 to -83 mV, approaching E (K) = -88 mV. The background K+ channels were insensitive to margotoxin (3 nM), apamine (3 nM), and clotrimazole (1 microM), high-affinity blockers of the lymphocyte Kv1.3, SKCa2, and IKCa1 channels. The current depended weakly on external pH. Arachidonic acid (20 microM) and Hg2+ (0.3-10 microM) suppressed background K+ current in Jurkat cells by 75-90%. Background K+ current was weakly sensitive to TEA+ (IC50 = 14 mM), and was efficiently suppressed by externally applied bupivacaine (IC50 = 5 microM), quinine (IC50 = 16 microM), and Ba2+ (2 mM). Our data, in particular strong inhibition by mercuric ions, suggest that background K+ currents expressed in Jurkat cells are mediated by TWIK-related spinal cord K+ (TRESK) channels belonging to the double-pore domain K+ channel family. The presence of human TRESK in the membrane protein fraction was confirmed by Western blot analysis.