Increased human red cell cation passive permeability below 12 degrees C.

The rate of most biological reactions declines as the temperature is reduced; indeed, cooling is often used to limit or terminate reactions. We report here a paradoxical temperature response of red cell K and Na permeability below 12 degrees C. This may be interpreted thermodynamically in terms of a membrane-ordering phenomenon, an observation supported by a variety of other physical measurements on red cell membranes reported in the literature.