Li/Na EXCHANGE AND Li ACTIVE TRANSPORT IN HUMAN LYMPHOID CELLS U937
CULTURED IN LITHIUM MEDIA
V.E. Yurinskaya, A.V. Moshkov, T.S. Goryachaya, A.A. Vereninov 1
Institute of Cytology RAS, St. Petersburg;
1 e-mail: verenino@gmail.com
Lithium transport across the cell membrane is interesting in the light of general cell physiology and because of its alteration during numerous human diseases. The mechanism of
Li+ transfer has been studied mainly in erythrocytes with a slow kinetics of ion exchange and therefore under the unbalanced ion distribution. Proliferating cultured cells with a
rapid ion exchange have not been used practically in study of Li+ transport. In present paper, the kinetics of Li+ uptake and exit as well as its balanced distribution
across the plasma membrane of U937 cells were studied at minimal external Li+ concentrations and after the whole replacement of external Na+ for Li+.
It has been found that a steady state Li+ distribution is attained at a high rate similar to that for Na+ and Cl- and that
Li+/Na+ discrimination under the balanced ion distribution at 1-10 mM external Li+ keeps on 3 and drops to 1 following blocking of the Na,K-ATPase
pump by ouabain. About of 80 % of the total Li+ flux across the plasma membrane under the balanced Li+ distribution at 5 mM external Li+ accounts
for the equivalent Li+/Li+ exchange. The most part of the Li+ flux into the cell down the electrochemical gradient is a flux through channels and its small part may
account for the NC and NKCC cotransport influxes. The downhill Li+ influxes are balanced by the uphill Li+ efflux involved in Li+/Na+
exchange. The Na+ flux involved in the coun-tertransport with the Li+ accounts for about 0.5 % of the total Na+ flux across the plasma membrane.
The study of Li+ transport is an important approach to understand the mechanism of the equivalent Li+/Li+/Na+/Na+
exchange because no blockers of this mode of ion transfer are known and it cannot be revealed by electrophysio-logical methods. Cells treated with the medium where Na+ is
replaced for Li+ are recommended as an object for studying cells without the Na,K-ATPase pump and with very low intracellular Na+ and K+ concentration.
Key words: Li+/Na+ exchange, lithium, ion transport, U937 cells
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