Synaptic membrane aging in the central nervous system.

Membrane potentials involved in neuronal excitability, transmitter uptake and so on were determined using synaptosomes from different age groups of mice. Synaptosomal resting membrane potential was found to decrease significantly in senescence. Concomitantly decreased activity of an electrogenic enzyme, Na+,K(+)-ATPase, was interpreted by two mechanisms. In senescence, the decreased content of phosphatidylcholine seemed responsible in part for decreased enzyme activity due to the modified lipid microenvironment. In the late stages of senescence, decreased enzyme content may rather cause reduction of enzyme activity, leading to a less negative set point of the membrane potential.