New Data on the Regulation of Taurine Uptake in Cultured Nervous Cells

Abstract

Uptake of taurine by different tissues or cell types has been extensively studied these last decades (8,10,20). The high affinity taurine uptake displayed by the majority of the cells studied is a Na⁺, Cl⁻ dependent system. Various hormones, drugs, and amino acids have been shown to affect this uptake. These compounds have been very often tested in vitro on cells in culture. However, they were usually tested by addition to the incubation media used for testing the taurine uptake. Some of these incubation media contain HEPES (N,N’hydroxyethylpiperazineethane sulfonate), which shows structural similarities with taurine (2-aminoethane sulfonate). We have previously shown that HEPES inhibits the taurine uptake of rat glial cells in primary cultures. This occurs by two mechanisms (11,12). A fast inhibition (within a few minutes) is observed when a Krebs-Ringer buffer supplemented with HEPES is used for the incubation of cells during taurine uptake determinations. On the contrary, when the glial cells are grown for a few days in a culture medium buffered with HEPES, instead of the more normal Na⁺ bicarbonate system, an inhibition of the taurine uptake is observed when cells are tested in the Krebs-Ringer incubation medium (11). This inhibition increases slowly with the culture length in the presence of HEPES (11). These results suggest the existence of two different mechanisms; a fast one (F) and a slow one (S), which may depend on the exposure time and conditions, and by which taurine uptake could be modulated. Different taurine analogs such as guanidinoethane sulfonate β-alanine, or hypotaurine are generally used to characterize the uptake of taurine by cultured cells by addition to the incubation media used for taurine uptake measurements. We have compared the effects obtained for these compounds on the taurine uptake upon addition to either the culture media (S condition) or the incubation media (F condition).