POSTNATAL ALTERATIONS IN EFFECTS OF POTASSIUM ON UPTAKE AND RELEASE OF GLUTAMATE AND GABA IN RAT BRAIN CORTEX SLICES

Abstract

Abstract— The uptake and release of glutamate and of GABA, as well as the effect of high potassium concentrations (35 or 80 mM) hereupon, were studied by aid of 14 C‐labelled amino acids in brain cortex slices from rats of different ages between birth and adulthood. Both the extent of the uptake (i.e. the tissue/medium ratio of 14 C at, or close to, equilibrium) and the rate of uptake (i.e. the tissue/ medium ratio of 14 C after short (5 min) incubation periods) increased with age. Differences were, however, found between glutamate and GABA, and the extent of the GABA uptake had a distinct maximum during the second postnatal week. At all ages, high concentrations of potassium caused a decrease in the rate of GABA uptake but were without effect on the rate with which glutamate was taken up. The release of the two amino acids occurred with approximately the same half‐time (50 min) in slices from animals of at least 14 days of age. Before that time the release of glutamate was somewhat faster, whereas that of GABA was much slower, especially during the first postnatal week (half‐time 90 min). The ontogenetic alterations in the effect of excess potassium were complex and varied both between the two potassium concentrations used and between the two amino acids. The results are thus compatible with the existence of different transport systems for the two amino acids, They also suggest that glutamate may exert other functions in addition to its role as a putative transmitter.