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.


METHODS
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 (Km) 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 Km 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 Km 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.
Carr
S J
SJ
Department of Medicine and Therapeutics, University of Leicester, UK.
Sikand
K
K
Moore
D
D
Norman
R I
RI
D017920:Antiporters / Q000378:metabolism*; D004910:Erythrocyte Membrane / Q000378:metabolism / Q000502:physiology*; D005260:Female; D005454:Fluorescence Polarization; D006801:Humans; D006973:Hypertension / Q000097:blood* / Q000188:drug therapy / Q000235:genetics; D008051:Lipid Bilayers / Q000378:metabolism; D008094:Lithium / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D010375:Pedigree; D012964:Sodium / Q000378:metabolism*; D014783:Viscosity
D017920:Antiporters; D008051:Lipid Bilayers; C045885:sodium-lithium countertransporter; D008094:Lithium; D012964:Sodium