ALTERED MEMBRANE MICROVISCOSITY IN ESSENTIAL-HYPERTENSION - RELATIONSHIP WITH FAMILY HISTORY OF HYPERTENSION AND SODIUM-LITHIUM COUNTERTRANSPORT ACTIVITY

Objective: To investigate the alterations in erythrocyte ghost membrane microviscosity in essential hypertensive patients and to determine the relationship between these changes and the sodium-lithium countertransport activity as a sensitive marker of membrane function. Subjects: Forty-three normolipidaemic essential hypertensive patients (23 treated, 20 untreated) and 27 normotensive controls were studied. Patients were attending the hospital hypertension clinic or a local general practitioner's surgery. Methods: Erythrocyte sodium-lithium countertransport activity was measured. The Michaelis constant (K-m) for extracellular sodium and maximal reaction velocity for sodium-lithium countertransport were measured in a subgroup consisting of 22 essential hypertensive patients and 11 normotensive controls. Erythrocyte membrane microviscosity was measured using fluorescence polarization anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1-[4-trimethylammoniumphenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH). Results: There was no significant difference in the fluorescence polarization anisotropy of DPH or TMA-DPH between normotensive and essential hypertensive patients. However, the fluorescence polarization anisotropy of TMA-DPH was increased significantly (reflecting increased membrane microviscosity) in hypertensive patients with a family history of hypertension compared with in patients without a family history of hypertension. The standard sodium-lithium countertransport activity was elevated in essential hypertensive patients compared with normotensive controls, and the K-m for sodium was significantly lower in patients with a family history of hypertension than in patients without a family history of hypertension. Patients with a family history of hypertension were clustered, with significantly lower K-m for sodium and higher TMA-DPH anisotropies than either hypertensive patients without a family history of hypertension or normotensive controls. Conclusions: These findings suggest that a high membrane microviscosity affecting the outer region of the lipid bilayer is associated with altered sodium-lithium countertransport kinetics in a subgroup of essential hypertensive patients consisting of those with a family history of hypertension.