Kinetics of and rate equations for the uptake of alpha-amino-isobutyric aicd and gamma-aminobutyric acid by mouse brain slices incubated in a glucose-free medium containing pyruvate as the energy source.

Mouse cerebrum slices were incubated in a medium containing pyruvate instead of glucose as the energy source. After a preincubation period alpha-aminoisobutyric acid (AIB) or gamma-aminobutyric acid (GABA) was added, and the rate of uptake by the slices was measured. AIB and GABA are taken up to above their concentration in the medium. Although influx is slower, the rate equation is the same as that for influx from a glucose medium; namely v = Vmax/1 x Kt/S) + kuS, where v = rate of uptake, S = concentration of AIB or GABA in the medium, and Vmax, Kt, and Ku are constants. The equation shows two parallel pathways for concentrative uptake, one saturable and one unsaturable. The uptake systems for AIB and GABA are qualitatively different. The maximum rate of uptake of AIB by the saturable component is the same in both media even though, in the pyruvate medium, AIB is bound less strongly to the 'carriers'. The maximum rate of uptake of GABA by the saturable component is less in the pyruvate medium although GABA is bound somewhat more strongly to the 'carriers'. The temperature coefficients of the kinetic parameters and their corresponding energies were determined for GABA. Going from glucose to pyruvate medium has little effect on the Arrhenius activation energy (Ea) associated with Vmax and the heat of reaction (delta H) associated with Kt but increases Ea associated with Ku by 1140%.