Membrane abnormality of erythrocytes is highly dependent on salt intake and renin profile in essential hypertension: an electron spin resonance study.

The purpose of the present study was to investigate membrane fluidity in essential hypertension using electron spin resonance (ESR) and spin-labelling. Erythrocytes from patients with untreated essential hypertension were examined and compared with age-matched normotensive subjects. The values of outer hyperfine splitting (2T') and order parameter (S) of the ESR spectra for a fatty acid spin label agent (5-nitroxy stearate) were significantly higher in essential hypertension than in the normotensive subjects. However, these values were not changed in secondary hypertension. This finding indicates that the membrane fluidity of erythrocytes was lower in essential hypertension. Further, the abnormality was attenuated with low-salt intake, and, on the contrary, was more prominent with high-salt intake in essential hypertension. Calcium loading to erythrocytes in vitro caused a greater decrease in the membrane fluidity in essential hypertension than in the normotensive controls. This calcium-induced change in the membrane fluidity was significantly inversely correlated with the value of plasma renin activity in essential hypertension. These results suggest that abnormality in the membrane fluidity might be emphasized in the presence of calcium, especially in low-renin essential hypertension, implying enhanced calcium sensitivity in this type of hypertension.