Validation of red cell sodium-lithium countertransport measurement--influence of different loading conditions.
Increased sodium-lithium countertransport in erythrocytes from patients with long-standing type I (insulin-dependent) diabetes mellitus has been considered as an early marker of nephropathy. Since the activity and kinetics of the sodium-lithium countertransport may critically depend on loading conditions, this study was aimed at determining sodium-lithium countertransport activity, Michaelis constant Km and maximum velocity Vmax in erythrocytes loaded in two different Li+ solutions. Sodium-lithium countertransport activity was determined in erythrocytes in 8 healthy control subjects after loading with 150 mmol/l LiCl compared with those loaded with 150 mmol/l LiHCO3. Sodium-lithium countertransport activity was similar for both loading procedures, although the erythrocyte lithium content did significantly differ (mean +/- SEM, 7.0 +/- 0.5 for LiCl and 8.9 +/- 0.5 mmol/l of cells for 150 mmol/l LiHCO3). There were no significant changes in the Km and Vmax. Increase of osmolality in efflux media containing 200 and 250 mmol/l NaCl resulted in a negligible shrinking of the red blood cells, not exceeding 2.2%. The main advantage is the short loading time of 15 min for LiHCO3 compared with 3 hours for LiCl. Under these conditions saturating intracellular Li+ concentrations can be obtained much more rapidly than with LiCl loading, thereby minimising alterations of the cell membranes. LiHCO3 loading shortens the experimental time considerably and enables a greater number of samples to be screened from larger population cohorts.
Besch
W
W
Institut für Diabetes, Gerhardt Katsch, Ernst-Moritz-Arndt-Universität Greifswald, Karlsburg, Germany.
Schläger
D
D
Brahm
J
J
Kohnert
K D
KD
D000328:Adult; D017920:Antiporters / Q000097:blood*; D002478:Cells, Cultured; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D008094:Lithium; D015203:Reproducibility of Results; D012964:Sodium / Q000494:pharmacology; D013997:Time Factors
D017920:Antiporters; C045885:sodium-lithium countertransporter; D008094:Lithium; D012964:Sodium