Three uptake systems in synaptosomes for nipecotic acid and beta-alanine.

An earlier finding that three systems were responsible for the uptake of gamma-aminobutyric acid by synaptosomes was corroborated. In addition, the existence of three uptake systems for RS-nipecotic acid and beta-alanine was demonstrated. We have called these systems high affinity, medium affinity and low affinity uptake systems respectively. In the case of all three substrates, the high affinity system Km values were around 1 microM or less, the medium affinity system Km values were in the range 10-46 microM, and the low affinity system Km values were in the range 290-3400 microM.