Temperature sensitivity of potassium flux into red blood cells in the familial pseudohyperkalaemia syndrome.

The temperature dependence of potassium flux into the red cells of normal and pseudohyperkalaemic individuals over the range 4-40 degrees C was measured using 86RbCl as tracer. Flux through the pump was measured as the ouabain-sensitive component (0.2 mM ouabain) and flux via Na+,K+-cotransport was measured as the decrease in the rate of K+ influx in the presence of 1 mM furosemide. The residual passive permeability of the red cell plasma membranes to K+ was that influx which was unaffected by either inhibitor. When Na+ influxes were measured, the ratio of Na+ to K+ transported via the furosemide-sensitive component was 1 over the full temperature range studied. The temperature sensitivity of K+ influx via the pump was normal as was the enzymic activity of the Na+,K+-ATPase. In contrast, the activity of the Na+,K+-cotransport system in pseudohyperkalaemics was more temperature sensitive than that of controls and affected individuals also showed a greater passive permeability to K+ at low temperatures. Red cell membranes from affected individuals have significantly increased amounts of phosphatidylcholine which are balanced, to a degree, by a decreased content of phosphatidylethanolamiane. It is proposed that in this example of familial pseudohyperkalaemia there is an alteration in the structure of the red cell plasma membrane which influences the temperature sensitivity of both its cotransport and passive permeability properties.