Effects of ouabain on membrane fluidity of erythrocytes in essential hypertension. An electron spin resonance study.

In the present study, we have examined the effects of ouabain on membrane fluidity of erythrocytes by use of an electron spin resonance (ESR) and spin-labeling method, and elucidated a possible role of Na+, K(+)-ATPase in the regulation of membrane fluidity in hypertension. Erythrocytes obtained from patients with essential hypertension were examined compared with those from age-matched normotensive subjects, and the ESR spectra for 5-nitroxy stearate incorporated into erythrocyte membranes were studied. The values of outer hyperfine splitting and order parameter (S) of the ESR spectra were significantly higher in patients with essential hypertension than in normotensive subjects. This finding shows that the membrane fluidity of erythrocytes might be lower in essential hypertension. Ouabain loading to erythrocytes decreased the membrane fluidity (S value was increased). The alternative degree was significantly greater in essential hypertension than in normotensive subjects. These results demonstrate that the membrane fluidity of erythrocytes might be highly dependent on the Na+, K(+)-ATPase activity in essential hypertension, which would suggest an abnormality in Na(+)-related cellular functions in hypertension.