Biomedical subjects

A C Yu

Publications and source records attributed to A C Yu.

39 records · Page 3Linked to original sources

PubMed1982

Uptake of glutamate, GABA, and glutamine into a predominantly GABA-ergic and a predominantly glutamatergic nerve cell population in culture.

Uptake kinetics for glutamate, GABA, and glutamine were determined in primary cultures of cerebral neurons, a predominantly GABA-ergic cell population, and of cerebellar granule cells, a predominantly glutamatergic cell population. A specially high Vmax for GABA uptake into the former and for glutamate uptake into the latter cells suggests that considerable amounts of released transmitters may be reaccumulated into appropriate nerve terminals. Nevertheless, the glutamate uptake into the cerebellar granule cells was less intense than that previously observed into corresponding cultures of astrocytes, whereas GABA was accumulated more intensely into neurons than into astrocytes. This suggests that especially glutamatergic neurons may be depleted for their transmitter by accumulation into adjacent astrocytes. If a glutamine flow astrocytes back to neurons served the purpose of balancing this transfer, it should be expected that glutamine accumulation was more intense in the glutamatergic than in the GABA-ergic cell population. This was not the case, suggesting that such a glutamate-glutamine cycle may not be operating to a major extent.

Animals↗

PubMed1982

Metabolic fate of 14C-labeled glutamate in astrocytes in primary cultures.

The metabolic fate of L-[U-14C]- and L-[1-14C]glutamate was studied in primary cultures of mouse astrocytes. Conversion of the uniformly labeled compound to glutamine and aspartate was followed by determination of specific activities after dansylation with [3H]dansyl chloride and subsequent thin layer chromatography of the dansylated amino acids. Metabolic fluxes were calculated from the alterations of specific activities and the pool sizes, which were likewise measured by a dansylation method. Formation of 14CO2 from [1-14C]glutamate was determined by the trapping of CO2 in hyamine hydroxide in a gas-tight chamber, which is, in the known absence of glutamate decarboxylase activity in the cultured astrocytes, an unequivocal expression of the metabolic flux via alpha-ketoglutarate to CO2 and succinyl-CoA. The metabolic fluxes determined by these procedures amounted to 2.4 nmol/min/mg protein for glutamine synthesis, 1.1 nmol/min/mg protein for aspartate production, and 4.1 nmol/min/mg protein for formation and subsequent decarboxylation of alpha-ketoglutarate. The latter process was unaffected by virtually complete inhibition of glutamate-oxaloacetic transaminase with aminooxyacetic acid, indicating that the formation of alpha-ketoglutarate occurs as an oxidative deamination rather than as a transamination. This suggests that the formation of alpha-ketoglutarate from glutamate represents a net degradation, not an isotopic exchange.

Amino Acids↗

PubMedDate not supplied

Metabolic fate of [U-14C]-labeled glutamate in primary cultures of mouse astrocytes as a function of development.

The metabolic fate of [U-14C]-labeled glutamate in astrocytes grown in primary cultures for 1-3 weeks in the absence or presence of dibutyryl cyclic AMP was followed using dansylation with 3H-dansyl chloride and subsequent thin layer chromatography of the dansylated amino acids. No indication was found of classical metabolic compartmentation, i.e., the specific radioactivity of glutamine (14C/3H ratio) never exceeded that of its precursor, glutamate. In accordance with a relatively late maturation of glutamine synthetase activity the rate of formation of labeled glutamine was much faster in 3-week-old than in 1-week-old cultures. The opposite was found for aspartate formation, but under all conditions incorporation of radioactivity into aspartate was pronounced.

Animals↗