High-affinity transport of gamma-aminobutyric acid, glycine, taurine, L-aspartic acid, and L-glutamic acid in synaptosomal (P2) tissue: a kinetic and substrate specificity analysis.
In a cortical P2 fraction, [14C]gamma-aminobutyric acid ([14C]GABA), [14C]glycine, [14C]taurine, and [14C]glutamic and [14C]aspartic acids are transported by four separate high-affinity transport systems with L-glutamic acid and L-aspartic acid transported by a common system. GABA transport in cortical synaptosomal tissue occurs by one high-affinity system, with no second, low-affinity, transport system detectable. Only one high-affinity system is observed for the transport of aspartic/glutamic acids; as with GABA transport, no low-affinity transport is detectable. In the uptake of taurine and glycine (cerebral cortex and pons-medulla-spinal cord) both high- and low-affinity transport processes could be detected. The high-affinity GABA and high-affinity taurine transport classes exhibit some overlap, with the GABA transport system being more specific and having a much higher Vmax value. High-affinity GABA transport exhibits no overlap with either the high-affinity glycine or the high-affinity aspartic/glutamic acid transport class, and in fact they demonstrate somewhat negative correlations in inhibition profiles. The inhibition profiles of high-affinity cortical glycine transport and those of high-affinity cortical taurine and aspartic/glutamic acid transport also show no significant positive relationship. The inhibition profiles of high-affinity glycine transport in the cerebral cortex and in the pons-medulla-spinal cord show a significant positive correlation with each other; however, high-affinity glycine uptake in the pons-medulla-spinal cord is more specific than that in the cerebral cortex. The inhibition profile of high-affinity taurine transport exhibits a nonsignificant negative correlation with that of the aspartic/glutamic acid transport class.
D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism; D001692:Biological Transport; D001933:Brain Stem / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism*; D005971:Glutamates / Q000378:metabolism; D018698:Glutamic Acid; D005998:Glycine / Q000378:metabolism; D007700:Kinetics; D051379:Mice; D008807:Mice, Inbred BALB C; D018377:Neurotransmitter Agents / Q000378:metabolism*; D013116:Spinal Cord / Q000378:metabolism; D013379:Substrate Specificity; D013574:Synaptosomes / Q000378:metabolism; D013654:Taurine / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D000596:Amino Acids; D005971:Glutamates; D018377:Neurotransmitter Agents; D013654:Taurine; D001224:Aspartic Acid; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D005998:Glycine