Studies of High Potassium and Low Potassium Sheep Erythrocyte Membrane Sodium-Adenosine Triphosphatase: INTERACTIONS WITH OLIGOMYCIN, ADENOSINE TRIPHOSPHATE, SODIUM, AND POTASSIUM

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Abstract The effects of oligomycin on Na+-ATPase of high K (HK) and low K (LK) sheep erythrocyte membranes have been investigated. Activation of LK Na+-ATPase is observed with ATP ≤ 0.2 µm; activation of HK is observed with ATP ≤ 0.02 µm. Inhibition occurs with higher ATP. At 0.2 µm ATP, oligomycin stimulation of LK Na+-ATPase is associated with a 3- to 4-fold increase in the 32P-intermediate; inhibition of HK is associated with only a slight increase (1.3-fold) in 32P-intermediate. The effects of oligomycin are similar for HK and LK in that activation occurs at low catalytic rates (≤ 20 pmoles mg-1 min-1); inhibition occurs at higher rates, irrespective of the means of altering the rate (varying ATP or Na+ concentration, or both; stimulation of LK with specific isoimmune antiserum). Oligomycin counteracts K+-inhibition (LK) and K+ counteracts oligomycin inhibition (HK). The results are consistent with a reaction sequence involving oligomycin-sensitive conformational changes of phosphorylated and probably unphosphorylated intermediate, i.e. [see PDF for equation] and [see PDF for equation] the resulting shift in equilibrium can, at low catalytic rates, be evidenced in stimulation of Na+-ATPase. Interaction of HK and LK Na+-ATPase with Na+, K+, and ATP are interdependent and markedly different for the two; at constant ATP (0.2 µm), HK is more sensitive to activation by Na+ and less sensitive to inhibition by K+ than LK ATPase. Although effects of both K+ and oligomycin are dependent on ATP concentration, a difference in affinity for ATP in addition to, or as a result of, a different relative affinity for Na+ and K+ may be the basis for the distinctions between HK and LK membranes.