Modification of taurine and hypotaurine uptake systems in cultured primary astrocytes by serum-free medium and dibutyryl cyclic AMP treatment

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Abstract
The characteristics of taurine and hypotaurine uptake were studied during astrocyte maturation in cultures grown in normal, serum-containing medium or in serum-free medium in the presence of 0.1 mmol/l dibutyryl cyclic AMP (dBcAMP). The uptake of both amino acids consisted of one saturable high-affinity component in both control and treated cultures. The dBcAMP treatment produced no marked modification of the transport systems. In the treated cultures the kinetic parameters of taurine and hypotaurine uptake remained unaltered during maturation. In the control cells the transport constant and maximal velocity of taurine uptake were greater in 21-day-old than in 16-day-old cultures, while the changes in hypotaurine transport were the opposite. The uptakes were strictly sodium-dependent and also considerably decreased when potassium ions were omitted from incubation medium. The uptake of both amino acids was affected more by potassium omission in the dBcAMP-treated than in the control cultures. Also the results with metabolic poisons suggest that physiological ion gradients sustained by an active Na(+), K(+)-pump are essential for the normal uptake of taurine and hypotaurine.