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Open Access Publications from the University of California

Voltage-gated and Ca2+-activated K+channels in intact human T lymphocytes: Noninvasive measurements of membrane currents, membrane potential, and intracellular calcium

  • Author(s): Verheugen, JAH
  • Vijverberg, HPM
  • Oortgiesen, M
  • Cahalan, MD
  • et al.

Voltage-gated n-type K(V) and Ca2+-activated K+[K(Ca)] channels were studied in cell-attached patches of activated human T lymphocytes. The single-channel conductance of the K(V) channel near the resting membrane potential (Vm) was 10 pS with low K+solution in the pipette, and 33 pS with high K+solution in the pipette. With high K+pipette solution, the channel showed inward rectification at positive potentials. K(V) channels in cell-attached patches of T lymphocytes inactivated more slowly than K(V) channels in the whole-cell configuration. In intact cells, steady state inactivation at the resting membrane potential was incomplete, and the threshold for activation was close to Vm. This indicates that the K(V) channel is active in the physiological Vmrange. An accurate, quantitative measure for Vmwas obtained from the reversal potential of the K(V) current evoked by ramp stimulation in cell-attached patches, with high K+solution in the pipette. This method yielded an average resting Vmfor activated human T lymphocytes of -59 mV. Fluctuations in Vmwere detected from changes in the reversal potential. Ionomycin activates K(Ca) channels and hyperpolarizes VmtO the Nernst potential for K+. Elevating intracellular Ca2+concentration ([Ca2+]i) by ionomycin opened a 33-50-pS channel, identified kinetically as the CTX-sensitive IK-type K(Ca) channel. The Ca2+sensitivity of the K(Ca) channel in intact cells was determined by measuring [Ca2+]iand the activity of single K(Ca) channels simultaneously. The threshold for activation was between 100 and 200 nM; half-maximal activation occurred at 450 nM. At concentrations > 1 µM, channel activity decreased. Stimulation of the T-cell receptor/CD3 complex using the mitogenic lectin, PHA, increased [Ca2+]i, and increased channel activity and current amplitude resulting from membrane hyperpolarization. © 1995, Rockefeller University Press., All rights reserved.

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