Characterization of the Erythrocyte Sodium-Lithium Countertransporter: Limitations and Assumptions of Traditional and Kinetic Methodologies

Characterization of the Erythrocyte Sodium-Lithium Countertransporter: Limitations and... The present work examined the key elements featuring in the various methods used to characterize the erythrocyte sodium-lithium countertransport. Effects of medium composition on lithium efflux were investigated in 20 subjects. Mean lithium efflux (mmol Li/l RBC.h) into a 150 mm sodium medium was significantly higher than efflux into a revised sodium-rich medium (149 mm) containing 1 mm Mg (0.335 ± 0.100 vs. 0.298 ± 0.085 respectively; P < 0.03). Mean lithium efflux into sodium-free media where sodium had been entirely replaced by magnesium, was significantly lower than efflux into a choline-based medium containing only 1 mm magnesium (0.088 ± 0.027 vs. 0.109 ± 0.034 respectively; P= 0.03). Sodium-lithium countertransport activity and the transporter's kinetic profile were measured simultaneously in 35 subjects using traditional choline-based and kinetic methodologies. There was a significant correlation between countertransport activity and maximal rate of turnover (V max) (r= 0.62; P < 0.001); V max values were consistently greater than their corresponding countertransport activities (P < 0.001). On subdividing the subject group into tertiles based on the Michaelis-Menten constant (k m ) values (mm), <75, 75 − 150 and >150, the slopes of the regression lines for each group diminished progressively (0.64, 0.49 and 0.23 respectively), correlations within each group remained significant (P < 0.001, P < 0.001 and P < 0.02). No significant correlation was found between k m values and countertransport activity (r= 0.035; P=ns). http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Membrane Biology Springer Journals

Characterization of the Erythrocyte Sodium-Lithium Countertransporter: Limitations and Assumptions of Traditional and Kinetic Methodologies

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Publisher
Springer-Verlag
Copyright
Copyright © Inc. by 1998 Springer-Verlag New York
Subject
Life Sciences; Biochemistry, general; Human Physiology
ISSN
0022-2631
eISSN
1432-1424
D.O.I.
10.1007/s002329900326
Publisher site
See Article on Publisher Site

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