High potassium and low potassium erythrocytes in cattle.

1. The K and Na concentrations in red blood cells (R.B.C.) of 251 animals of the Simmenthal breed and thirty-two animals of other cattle breeds were measured. [Na](cells)+[K](cells) was 89.4 m-mole/l. cells. [K](cells) varied between 7 and 70 and [Na](cells) varied in the inverse sense between 15 and 87 m-mole/l. cells.2. The frequency distribution of animals according to K content of R.B.C.S, which could best be fitted by two superimposed Gaussian curves, suggests that there are two distinct types of cells (high K (HK) cells and low K (LK) cells). Animals with HK cells were considerably less frequent than animals with LK cells.3. Differences in breed, age or sex do not account for the difference in cation content of R.B.C.S.4. Cold stored or PCMBS-treated HK cells show a more vigorous cation pump activity than equally treated LK cells.5. At a Na concentration of 100 mM and a K concentration of 10 mM isolated haemoglobin-free membranes prepared from HK cells exhibit a higher activity of Na+K stimulated (ouabain inhibitable) ATPase activity per mg of protein than membranes from LK cells.