Transport of L-proline by rat brain slices.

L-Proline is taken up into slices of rat cerebral cortex by a structurally specific 'high affinity' system which is absolutely dependent on sodium ions. The system mediating L-proline uptake in homogenates of cerebral cortex is associated with osmotically sensitive particles of the same equilibrium density as synaptosomes. Based on tissue-medium ratios, the uptake of L-proline is most efficient in slices of cerebral cortex and of hypothalamus, and least efficient in slices of cerebellum. L-Proline taken up into slices of cerebral cortex can be released from these slices by an increased potassium ioort into and out of brain slices are consistent with L-proline functioning as a synaptic transmitter in that they are analogous to observations on the transport of transmitter amino acids such as GABA.