Comparative properties of high potassium and low potassium sheep erythrocyte membrane sodium-activated adenosine triphosphatase.

A comparative study of the Na+-stimulated adenosine triphosphatase system in high potassium (HK) and low potassium (LK) sheep red cell membranes was carried out. For HK:LK activity, the approximate ratios were as follows: 10 for Na+-ATPase, 13 for Na+, K+-ATPase, and 2.7 for [%+ ADP-ATP exchange activity; the ratio of Na+-stimulated membrane phosphorylation was approximately 7. With Na+ present, Kf at concentrations below 5 mM stimulated ATPase activity in HK membranes but not in LK membranes; above 5 mM, K+ inhibited Na+-ATPase, to an extent much greater in LK than HK membranes. [14C]ADP-ATP exchange in the presence of Na+ and oligomycin was similarly inhibited by K+, markedly in LK, but only slightly in HK membranes. These observations are consistent with data reported for the Na+, K+ pumping activity in HK and LK cells described by D. C. Tosteson (in G. A. JAMIESON AND T. J. GREENWALT (Editors), Red cell membrane, structure and funcfion. J. B. Lippincott Company, Philadelphia, 1969, p. 291) and P. G. Hoffman (Ph.D. thesis, Duke University, 1969), and provide evidence at the molecular level for the physiological differences in activity between HK and LK cells.