Functional expression of the Na/K pump is controlled via a cyclosporin A-sensitive signalling pathway in activated human lymphocytes.

An immunosuppressant cyclosporin A (CsA) inhibits T-cell proliferation by blocking the nuclear factor of activated T-cells (NFAT) required for expression of the interleukin-2 (IL-2) gene. This work has demonstrated for the first time that in human blood lymphocytes (HBLs) activated by phytohemagglutinin (PHA), CsA at anti-proliferative doses inhibits the late sustained increase in ouabain-sensitive Rb(K) influxes, which accompanies the growth phase of G0/G1/S transition. CsA affects neither the initial, transient activation of the pump in response to PHA nor the ouabain-resistant ion fluxes during cell cycle progression. When the HBLs were rendered competent to proliferate by phorbol 12,13-dibutyrate ester and ionomycin in the presence of CsA, the exogenous IL-2 did not bypass the initial inhibitory effect of CsA on the long-term pump enhancement. When applied after the competence induction, CsA produced no effect on the sustained increase in ouabain-sensitive Rb influxes during the IL-2-induced progression phase. These results indicate that in activated HBLs, (1) IL-2 is involved in functional expression of the Na/K pump during cell transition from quiescence to proliferation, (2) the cell cycle-associated upregulation of the pump is related to a CsA-sensitive signalling pathway.