Sodium-dependent proline uptake in the rat hippocampal formation: association with ipsilateral-commissural projections of CA3 pyramidal cells.
Na+-dependent uptake of L-[3H]proline was measured in a crude synaptosomal preparation from the entire rat hippocampal formation or from isolated hippocampal regions. Among hippocampal regions, Na+-dependent proline uptake was significantly greater in areas CA1 and CA2-CA3-CA4 than in the fascia dentata, whereas there was no marked regional difference in the distribution of Na+-dependent gamma-[14C]aminobutyric acid ([14C]GABA) uptake. A bilateral kainic acid lesion, which destroyed most of the CA3 hippocampal pyramidal cells, reduced Na+-dependent proline uptake by an average of 41% in area CA1 and 52% in area CA2-CA3-CA4, without affecting the Na+-dependent uptake of GABA. In the fascia dentata, neither proline nor GABA uptake was significantly altered. Kinetic studies suggested that hippocampal synaptosomes take up proline by both a high-affinity (KT = 6.7 microM) and a low-affinity (KT = 290 microM) Na+-dependent process, whereas L-[14C]glutamate is taken up predominantly by a high-affinity (KT = 6.1 microM) process. A bilateral kainic acid lesion reduced the Vmax of high-affinity proline uptake by an average of 72%, the Vmax of low-affinity proline uptake by 44%, and the Vmax of high affinity glutamate uptake by 43%, without significantly changing the affinity of the transport carriers for substrate. Ipsilateral-commissural projections of CA3 hippocampal pyramidal cells appear to possess nearly as great a capacity for taking up proline as for taking up glutamate, a probable transmitter of these pathways. Therefore proline may play an important role in transmission at synapses made by the CA3-derived Schaffer collateral, commissural, and ipsilateral associational fibers.
D000818:Animals; D005260:Female; D005971:Glutamates / Q000378:metabolism; D018698:Glutamic Acid; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism*; D007608:Kainic Acid / Q000494:pharmacology; D009434:Neural Pathways / Q000378:metabolism; D011392:Proline / Q000378:metabolism*; D011712:Pyramidal Tracts / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000494:pharmacology*; D013574:Synaptosomes / Q000378:metabolism; D014018:Tissue Distribution
D005971:Glutamates; D018698:Glutamic Acid; D011392:Proline; D012964:Sodium; D007608:Kainic Acid