Effect of plasma storage on erythrocyte sodium pump measurements

The possibility that sodium handling in red cells may be an indicator of abnormalities associated with hypertension has encouraged many investigators to study erythrocyte sodium transport. The results have often been in conflict, perhaps because of the variety of laboratory techniques and procedures employed. Investigation into the effect of storage of red cells in plasma showed larger changes when cells were stored at 0 degrees C than at room temperature (19 degrees). At 0 degrees C, sodium efflux via the pump increased 22.1% (p less than 0.001) after 2 hours storage and 54.2% (p less than 0.005) after 4 hrs of storage. At 19 degrees C, sodium efflux values were more scattered after storage, but the mean value was not significantly different even after 4 hours. Intracellular sodium increased 17.3% in cells stored 4 hrs at 0 degrees C; significant changes were not observed when cells were stored 2 hrs at 0 degrees C or 2-4 hours at 19 degrees C. The number of Na, K-ATPase sites per red blood cell did not change with either storage condition. For samples processed within one hour of drawing, or stored at room temperature, there were close correlations between the sodium efflux per site and the intracellular sodium concentration as well as between the intracellular sodium and the sites per red cell. These relationships were not evident for cells stored at 0 degrees C. These data indicate that red cells to be used in pump measurements should be stored at room temperature and should be processed within 2 hours.