Turnover of GABA by Infusion With Labeled Precursors

Turnover of GABA by Infusion with Labeled Precursors 

Glutamate is the immediate precursor for GABA in the brain. This acidic amino acid is, however, only poorly transported across the blood-brain barrier and cannot be administered systemically. When labeled glutamate is administered intracerebrally, it is rapidly taken up into the glial cells (Schon and Kelly, 1974) and converted to glutamine. The conversion of glutamate into GABA based on the relahve specific activity is poor (0.1-0.3) (Berl et al., 1961). 

If we assume that the precursor glutamate pool has a higher specific activity than the total glutamate pool, as indicated by postmortem studies, then the calculated rate of GABA synthesis from glutamate could be reduced correspondingly. 

The half-hfe was calculated from a first-order reaction decay rate and the turnover was the reaction rate constant multiplied by the amino acid level. 

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