GlyTs mediate the uptake of glycine from the extracellular space into the cytosol. They belong to a large family of NaC/ClK-dependent transporter proteins, which includes transporters for monoamines (serotonin, norepinephrine and dopamine) and the inhibitory neurotransmitter g-aminobutyric acid (GABA). These polytopic membrane proteins share a common transmembrane topology with 12 transmembrane domains (TMDs) connected by six extracellular and five intracellular loops.  Both GlyTs exist in multiple splice variants: three GlyT2 isoforms (a, b, c) differ in the N-terminal region, whereas three N-terminal (a, b, c) and two C-terminal (d, e) exons have been reported to generate different variants of GlyT1.  The transporters GLYTla, GLYTlb and GLYTlc have been isolated from the CNS of both rodents and humans. Two isoforms of the GLYT2 gene product have been reported and have been named GLYT2a and GLYT2b. The uptake of glycine mediated by GlyTs is energetically coupled to the transmembrane sodium gradient maintained by the NaC/KC-ATPase. Pharmacological evidence indicates that GLYT 1 transports glycine in the cerebral cortex, but that in the cerebellum, it shares this function with GLYT2.


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