K_bg and Kv1.3 channels mediate potassium efflux in the early phase of apoptosis in Jurkat T lymphocytes

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 K_bg and Kv1.3 channels to the transient and posttransient STS-induced K⁺ efflux components, respectively, was confirmed by the effects of bupivacaine, predominantly blocking K_bg current, and the Kv1.3-specific blocker margatoxin. Channel-mediated K⁺ efflux provoked a substantial cellular shrinkage and affected the activation of caspases.