Cyclosporin elicits a non-responsive state and a shift in K+ fluxes in the early phase of activation of human lymphocytes with anti-CD3

Study of membrane potential in T lymphocytes subpopulations using flow cytometry

Background

Ion channels are involved in the control of membrane potential (ψ) in a variety of cells. The maintenance of ψ in human T lymphocytes is essential for T-cell activation and was suggested to depend mostly on the voltage-gated Kv1.3 channel. Blockage of Kv1.3 inhibits cytokine production and lymphocyte proliferation in vitro and suppresses immune response in vivo. T lymphocytes are a heterogeneous cell population and the expression of Kv1.3 varies among cell subsets. Oxonol diBA-C4-(3) was used to determine ψ by flow cytometry. The presence of distinct T cell subsets was evaluated by immunophenotyping techniques and the contribution of Kv1.3 channels for the maintenance of ψ was investigated using selective blockers.

Results

The distribution of ψ in T lymphocytes varied among blood donors and did not always follow a unimodal pattern. T lymphocytes were divided into CD3⁺/CD45RO^- and CD3⁺/CD45RO⁺ subsets, whose peak channel values of ψ were -58 ± 3.6 mV and -37 ± 4.1 mV, respectively. MgTX (specific inhibitor of Kv1.3 channels) had no significant effect in the ψ of CD3⁺/CD45RO^- subsets but depolarized CD3⁺/CD45RO⁺ cells to -27 ± 5.1 mV.

Conclusion

Combination of optical methods for determination of ψ by flow cytometry with immuophenotyping techniques opens new possibilities for the study of ion channels in the biology of heterogeneous cell populations such as T lymphocyte subsets.

Cyclosporin A induces the opening of a potassium-selective channel in higher plant mitochondria

The immunosuppressive drug, cyclosporin A (CsA), induces the generation of a transmembrane electrical potential difference (deltapsi) in deenergized plant mitochondria incubated in sucrose-based media. Build up of deltapsi is prevented by external monovalent cations in the order K+ > Rb+ = Li+ > Na+, or by the protonophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone, which also collapses the deltapsi generated by CsA. Entry of K+ into mitochondria can be monitored as swelling by incubating the organelles in a medium containing KCl to maintain constant osmolarity. This swelling is inhibited by ATP and stimulated by CsA or valinomycin. In addition, in mitochondria energized by succinate, KCl causes a dissipation of deltapsi, with sigmoidal kinetics, which is favored by CsA. Therefore, plant mitochondria appear to possess a K+ selective, voltage-dependent channel, which is opened by CsA, regulated by the redox state, and inhibited by nucleotides. The hypothetical roles of this new K+ATP channel are discussed in relation to its potential involvement in mitochondrial volume regulation, thermogenesis, apoptosis, and/or prevention of reactive oxygen species formation in plants.