The temperature dependence of passive potassium permeability in mammalian erythrocytes

Abstract

The effect of temperature on the “passive” permeability of mammalian plasma membranes to K +, measured as the residual flux in the presence of ouabain and bumetanide, was investigated in erythrocytes of several species. Without Ca 2+ in the medium, only human red cells demonstrated the “paradoxical” rise in passive flux at low temperature (i.e., below 12 °C) seen by other workers. In the other species no such effect was apparent; K + influx decreased progressively with cooling down to 0 °C. Below 18.5 °C the apparent energy of activation ( E a ) was very low—close to that for free diffusion in water—for red cells of all species except human. Above 18.5 °C the E a was much greater and was also more variable amongst the red cells of the species chosen. Neither the inhibitors used nor cell volume changes during incubation accounted for the absence of the paradoxical effect in the species studied here. A rise in permeation of K + with cooling can, however, be produced by the addition of Ca 2+ to the medium, probably by activation of the Ca 2+-sensitive K + channel. This effect would account for previous reports of a paradoxical effect in dog and rat erythrocytes.