Uptake and metabolism of glutamate at non-synaptic regions of crayfish central nerve fibers: implications for axon–glia signaling

Synthesis and release of N-acetylaspartylglutamate (NAAG) by crayfish nerve fibers: implications for axon–glia signaling

“…As expected for this non-metabolized glutamate analog (Kane et al, 2000), there was no detectable radiolabeled NAAG.…”

“…b Percent of the sum of the radiolabeled compounds recovered in samples of axonal or glial cytoplasm averaged for each experimental pair. A. K. Urazaev et al 240 inhibitor and heteroexchange substrate of glutamate uptake in cray¢sh nerve cord (Kane et al, 2000), markedly increased the amount of radiolabel in superfusates within 4^5 min and for as long as 25 min, but did not increase radiolabel appearance in the superfusate upon nerve cord stimulation (indicated by the second arrow in Fig. 2).…”

“…Stimulation at 50 Hz was used to induce release of agents because at this frequency maximal glial cell hyperpolarization occurs (Lieberman et al, 1989). After incubation with the radiotracer, the nerve cord was washed with non-radioactive NCS for 15 min to remove extracellular label (Kane et al, 2000) and relocated to a three-compartment experimental chamber to measure release of radioactive compounds. The compartments were isolated by grease seals and independently superfused.…”

“…of the periaxonal glial sheath) was taken to be 8 Wm and the volume of glial cytoplasm was taken to be 45% of the total volume of glial sheath (Hargittai and Lieberman, 1991). Although glial cytoplasm represents only 5% of the total volume of axoplasm and gliaplasm combined, glia account for 75% of radiolabeled glutamate uptake (Kane et al, 2000) and 95% of O 2 consumption of the MGNF (Hargittai and Lieberman, 1991). To insure that comparisons of radiolabel uptake and distribution between axons and glia were representative of the true metabolic capacity of these two cellular compartments, volume calculations of axoplasm and glial cytoplasm were made and radiolabel content was normalized and expressed in units of counts/min/Wl cytoplasm.…”

“…The concentrations of radioactive glutamate, NAAG, glutamine, and aspartate (normalized to c.p.m./Wl of cytoplasm) were much higher (35^62-fold) in glial cytoplasm than in axoplasm (P 9 0.05). In absolute terms, the glial sheath typically accumulated 70^75% of the radiolabel (Kane et al, 2000).…”