Aging of membrane transport mechanisms in the central nervous system--high affinity choline transport in rat cortical synaptosomes.

High affinity choline transport has been studied in cortical synaptosomes from rats ranging from 2 months to 30 months of age. Initial velocities were measured as a function of both choline and sodium concentration. These data give similar fits to a kinetic model which was previously found to give minimal best fit to data from 2-month-old animals. Thus, aging has apparently not altered the fundamental mechanism by which carrier, sodium, and choline interact in the process of uptake. Although some small differences in initial velocities were found between data from young and older animals, these differences showed no pattern and were not statistically significant. It is concluded that the choline transporter is unaffected by age, in contrast to the transporters for GABA and glutamic acid, whose transport capacities were found to decline with age.