Platelet membrane properties in Alzheimer and multi-infarct dementias.

Recent investigations revealed that the physical properties of both central and peripheral cell membranes are changed in dementia of the Alzheimer Type (DAT). We attempted to ascertain whether this effect is specific for DAT by studying the polarization of diphenylhexatriene (DPH) fluorescence (an indicator of membrane "microviscosity") in the membranes of platelets isolated from DAT patients, patients with multi-infarct dementia and healthy controls. The 3 groups were matched as closely as possible for age and sex distributions. Platelet phospholipid composition was also examined in an attempt to identify the chemical basis of the membrane change(s). These studies revealed that DPH fluorescence polarization is significantly reduced in platelets from DAT patients, but not in patients with multi-infarct dementia, compared with controls. Analysis of the phospholipid composition of platelets from the 3 groups of subjects did not find any significant differences which might explain the change in membrane properties.