Taurine and beta-alanine uptake in primary astrocytes differentiating in culture: effects of ions.
The effects of ions on taurine and beta-alanine uptake were studied in astrocytes during cellular differentiation in primary cultures. The uptakes were strictly Na+-dependent and also inhibited by the omission of K+ and in the presence of ouabain suggesting that their transport is fuelled mainly by these cation gradients. Two sodium ions were associated in the transport of one taurine and beta-alanine molecule across cell membranes. A reduction in Cl- concentration also markedly inhibited the uptake of both amino acids, indicating that this anion is of importance in the transport processes. The similar ion dependency profiles of taurine and beta-alanine uptake corroborate the assumption that the uptake of these amino acids in astrocytes is mediated by the same carrier. In Na+- and K+-free media both taurine and beta-alanine uptakes were reduced significantly more in 14-day-old or older than in 7-day-old cultures. No significant changes occurred in the coupling ratio between Na+ and taurine or beta-alanine as a function of spontaneous cellular differentiation or upon dBcAMP treatment. These results suggest that the uptake systems of these structurally related amino acids in astrocytes have reached a relatively high degree of functional maturity by two weeks in culture.
Holopainen
I
I
Department of Biomedical Sciences, University of Tampere, Finland.
D000409:Alanine / Q000493:pharmacokinetics*; D000818:Animals; D001253:Astrocytes / Q000166:cytology / Q000378:metabolism*; D002454:Cell Differentiation; D002478:Cells, Cultured; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000494:pharmacology / Q000502:physiology*; D013654:Taurine / Q000493:pharmacokinetics*; D015091:beta-Alanine / Q000493:pharmacokinetics*
D015091:beta-Alanine; D013654:Taurine; D010042:Ouabain; D012964:Sodium; D000409:Alanine; D011188:Potassium