Effect of cyclosporine A on Na+/K(+)-ATPase, Na+/K+/2Cl- cotransporter, and H+/K(+)-ATPase in MDCK cells and two subtypes, C7 and C11.

We investigated the influence of cyclosporine A (CsA) on key plasma membrane ion transport systems Na+/K(+)-ATPase, Na+/K+/2Cl- cotransporter, and H+/K(+)-ATPase in MDCK cells and two subtypes, C7 and C11, serving as a model system to study principal (C7) and intercalated (C11) cell properties of the distal nephron. The transport activity of Na+/K(+)-ATPase was significantly decreased in all cell types on CsA administration (8 x 10(-6) M) for 2 days, whereas the protein levels of Na+/K(+)-ATPase alpha-subunit in plasma membranes isolated from MDCK, C7, and C11 cells remained unchanged. The transport activity of Na+/K+/2Cl- cotransporter was significantly inhibited by CsA only in MDCK and C11 cells, but again plasma membrane protein levels were not altered. In contrast, C7 cell plasma membranes showed an increase of transport protein content, although the Na+/K+/2Cl- cotransporter activity was not affected by CsA. The H+/K(+)-ATPase transport activity remained unchanged in all three cell types. These data indicate that in C7 cells CsA might induce insertion of transporters into the plasma membrane, thus compensating the decrease of transport activity observed in MDCK and C11 cells. Furthermore, CsA significantly inhibited cell proliferation at 4 x 10(-6) M for C7 and C11 cells and at 8 x 10(-6) M for MDCK cells. Proliferation was completely abolished at 1.6 x 10(-5) M CsA. After 48 h of CsA incubation, the intracellular sodium concentration increased in all three different cell types; however, it stayed within the physiological range of mammalian cells. We, therefore, suggest that CsA is capable of reducing Na+/K(+)-ATPase and Na+/K+/2Cl- cotransporter activities in cells of the distal nephron, thereby contributing to the hyperkalemia observed in patients treated with CsA.