The Primacy of Membrane Microviscosity in Genetic Hypertension

Because of the known influence of the lipid bilayer on membrane transport systems, the characteristics of the bilayer from vascular smooth muscle and from platelets were studied in genetically hypertensive and in normotensive rats. Membrane microviscosity was measured by the degree of polarization of embedded fluorophores. Both the core of the bilayer in which diphenylhexatriene (DPH) was embedded and the surface in which the trimethyl-ammonium derivative of DPH (TMA-DPH) was embedded evidence a greater microviscosity (less fluid) in the hypertensive than in the normotensive rat. We had previously observed that monovalent cation fluxes were elevated in hypertension. We now observe that an increase in calcium concentration reverses both the elevated microviscosity and the increased cation fluxes. Conversely an increased incorporation of cholesterol in the membrane increases both the microviscosity and the cation fluxes. We hypothesize that the greater microviscosity of the lipid bilayer in hypertension constitutes a generalized defect of the matrix in which the transport proteins function. We further hypothesize that this defect is responsible for the multiple abnormalities of membrane transport systems and the increase in vascular reactivity that have been described in genetic hypertension.