Characteristics of Amino Acid Accumulation by Synaptosomal Particles Isolated From Rat Brain

Abstract

—The characteristics of the accumulation of 14 L‐amino acids (Leu, Ileu, Val, His, Tyr, Phe, Gly, Ala, Ser, Thr, Asp, Pro, Arg and Lys) by synaptosomal fractions prepared from rat brains were studied. Distinct differences were observed in the ion requirements for the accumulation of these amino acids. The accumulation of Asp and Pro alone showed a total requirement for Na+; uptakes of the other amino acids were either maximal in Na+‐free media or only partially dependent on the presence of external Na+. With brain maturation, two types of developmental alterations could be distinguished: (1) changes in rates of influx, and (2) changes in the effects of ions. Synaptosomal fractions prepared from brains of immature rats accumulated Leu, Arg and Lys to a greater extent and Val, Tyr, Pro and Asp to a lesser extent than did the fractions prepared from brains of mature animals. The accumulation of Ser and Thr by immature fractions was partially dependent on external Na+, whereas their accumulation by adult fractions was Na+‐independent. These alterations in Na+ requirements coincided with developmental changes in mutual inhibitions of amino acid transport.

Preferred Stereoselective Transport of the D-isomer of cis-4-[18F]fluoro-proline at the Blood–Brain Barrier

“…The transport of L-proline in the brain has attracted considerable interest. More than 30 years ago, it was discovered that mammalian synaptosomes express a high-affinity, Na þ -dependent L-proline uptake activity similar to the synaptosomal uptake activities identified for recognized neurotransmitters, suggesting that L-proline might be a neurotransmitter or neuromodulator in the mammalian central nervous system (Bennett et al, 1972;Peterson and Raghupathy, 1972;Balcar et al, 1976;Hauptmann et al, 1983;Nadler, 1987). In 1992, cDNAs were isolated from rat and human brain that code for a high-affinity Na þ -dependent transporter designated PROT (Fremeau et al, 1992(Fremeau et al, , 1996Shafqat et al, 1995;Renick et al, 1999;Crump et al, 1999).…”

The Mammalian Brain High-Affinity l-Proline Transporter Is Enriched Preferentially in Synaptic Vesicles in a Subpopulation of Excitatory Nerve Terminals in Rat Forebrain

“…The pharmacological specificity, ion dependence, and kinetics of the cloned transporter expressed in nonneural cells (Fremeau et al, 1992(Fremeau et al, , 1996Shafqat et al, 1995) are similar to the corresponding properties of the high-affinity component of synaptosomal L-proline uptake (Bennett et al, 1972;Peterson and Ragupathy, 1972;Balcar et al, 1976;Nadler, 1987). These properties distinguish PROT from the other widely expressed Na ϩ -dependent plasma membrane carriers that transport L-proline, including the intestinal brush border "IMINO" carrier (Stevens and Wright, 1985) and the system "A" and system "ASC" neutral amino acid carriers (Christensen, 1990).…”

Role of sialic acid in synaptosomal transport of amino acid transmitters.

“…1. It is well documented that GABA is transported into synaptosomes on a separate carrier protein (28), whereas D-aspartate, anonmetabolizeable stereoisomer of aspartate (29) which is common to a number of acidic amino acids including L-glutamate (30)(31)(32)(33)(34)(35). Preincubation of synaptosomes with increasing concentrations of neuraminidase resulted in a progressive decrease in the rate of uptake of both amino acids.…”