Demonstration of temperature dependence of Na(+)-K+ pump activity of human blood cells.

In our physiology laboratory course we introduced several simple but instructive experiments in which medical students make observations on their own blood cells. In this experiment, students measured and discussed the effect of different temperatures on Na+ and K+ distribution between blood cells and plasma. In venous blood of 35 female and 64 male students, plasma (extracellular) [Na+] and [K+] were measured with ion-selective electrodes immediately after blood sampling and successively four times in intervals of 1 h in three samples stored at 1, 20, and 37 degrees C. At 1 degree C, plasma [K+] increased significantly and nearly linearly with cooling time of the blood, whereas plasma [Na+] decreased. In contrast, at 37 degrees C plasma K+ levels significantly decreased in the first 2 h and then stabilized at new levels clearly below baselines. At 1 degree C blood cells had a greater K+ loss in women than in men, whereas at 37 degrees C the K+ loss was significantly less pronounced in women. Plasma Na+ did not significantly change at 37 degrees C. This remarkably reproducible experiment demonstrates the existence of active Na(+)-K+ transport in human blood cells by showing medical students, with their own blood, that the basal chemical processes of such pumps are inhibited at a temperature of 1 degree C and stimulated when blood temperature is slightly higher than the usual body temperature.