Energetics of low affinity amino acid transport into brain slices

It appears possible to dissect and study some of the potential energy sources for amino acid transport in brain slices despite the apparent complexity of the tissue in comparison to that of isolated bacterial vesicles23. The uptake capability of the tissue may be inadvertently damaged in some experimental protocols so that very special controls must be used to ensure that the treatment did not somehow inactivate the very mechanism that thereafter will be tested. We have presented some evidence that brain slice amino acid transport may not be obligatorily linked to glycolysis, ATP levels, Na+, K+-ATPase activity, K+ levels or direction of flux, or to Na+ flux. However, the energy source linkage for different amino acids appears to be rather specific, so that further generalizations are difficult to sustain. For instance, the incubation media and conditions we describe here were experimentally adjusted to maximize uptake of D-glu or alpha-AIB in the absence of glucose, or in lowered K+ or Na+. Therefore, these procedures, the results of which directly challenge some common assumptions regarding the energy basis for active transport in brain slices, probably will not be universally extensible to all other actively transported amino acids.