Non-esterified fatty acids may regulate human leucocyte sodium pump activity

1. Human leucocyte sodium pump activity was studied in normal fasting subjects by measuring the ouabain-sensitive ²²Na⁺ efflux rate constants.

2. This ²²Na⁺ efflux rate constant was inversely related to the fasting plasma non-esterified fatty acid level (r_s = −0.73, P < 0.0001).

3. An oral glucose load (40 g/m² surface area) led to an increase in the leucocyte ouabain-sensitive ²²Na⁺ efflux rate constant after 2 h (1.97 ± 0.25 to 2.44 ± 0.19 h⁻¹, P < 0.0001, n = 11). There was a concomitant fall in the plasma non-esterified fatty acid level.

4. Incubation of leucocytes in vitro with 100 μmol/l linoleic acid inhibited the leucocyte ouabain-sensitive ²²Na⁺ efflux rate constant (1.52 ± 0.27 vs 0.84 ± 0.24 h⁻¹, P < 0.001, n = 8).

5. The leucocyte Na⁺,K⁺-dependent adenosine triphosphatase (Na⁺,K⁺-ATPase) activity was inhibited in vitro by long chain non-esterified fatty acids, especially when unsaturated.

6. Non-esterified fatty acids may account for some of the Na⁺,K⁺-ATPase inhibitory activity of plasma.