Abnormalities in membrane micro viscosity and ion transport in genetic muscular dystrophy

Abstract

WE have demonstrated recently several functional differences between membrane-bound enzymes from tissues of muscular dystrophic chicks and of controls¹. Several other membrane anomalies have been associated with this disease^2–7, but so far the only known biochemical anomaly in the affected membranes is a difference in lipid composition^8,9. This could cause all the observed functional defects, including those in enzyme activities and permeability, through an alteration in the membrane microenvironment¹⁰. Certain physical properties of the microenvironment can be studied by fluorescent polarisation techniques that measure the mobility of a lipid-soluble fluorescent dye^11,12. The basis for this approach is the fact that membrane cholesterol, which strongly affects the microviscosity of liposomes¹⁰, is present in significantly greater than normal amounts in genetic muscular dystrophy. Using this approach, we found (Table 1) that the membranes of muscle, liver and erythrocytes of dystrophic chicks have a significantly higher microviscosity than normal controls. The greatest difference was in muscle, the site of the clinical symptoms of this genetic disease. The higher cholesterol :phospholipid ratio characteristic of the diseased membrane is sufficient to account for the observed increase in microviscosity¹¹.