Abstract
New methods for determining the volume and sodium content of human mononucleated cells are presented and the kinetics of sodium efflux are characterized. Sodium efflux obeyed first-order kinetics with a half-life of about 9 min. The ouabain-sensitive sodium pump is responsible for about 60% of the total turnover of this cation. Reliable measurement of cell volume and sodium content requires pre-incubation at physiological conditions. Determination of sodium efflux should be based on the initial (less than 15 min) cellular delay of 22Na-activity in preloaded cells. In normal subjects (n=34), mean cell volume was 635±138 nl/106 cells and sodium content averaged 14.6±2.8 mmol/l cell. Total and ouabain-sensitive efflux rate constants were 4.56±0.66 h−1 and 2.70±0.47 h−1. Corresponding absolute sodium efflux averaged 65.1±14.8 and 38.9±9.6 mmol/l/h, respectively.
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