Effects of cations on taurine, hypotaurine, and GABA uptake in mouse brain slices.

The effects of cations on taurine, hypotaurine and GABA uptake were studied in mouse brain slices under identical experimental conditions. The uptakes were all strictly sodium-dependent. The omission or excess of K+ inhibited similarly taurine, hypotaurine and GABA uptake. The effects of omission of Ca2+ or Mg2+ were less pronounced. In both normal-sodium and low-sodium media all uptakes were saturable, consisting of both low- and high-affinity transport components. The Km constants for both low- and high-affinity transport components of hypotaurine and GABA increased in low-sodium medium, suggesting that sodium ions are necessary for their attachment to possible carrier sites in plasma membranes. In the case of taurine, however, the translation rate rather than the affinity of carrier sites was affected in Na+-free media. More than two sodium ions may be involved in the transport of one hypotaurine and one GABA molecule, whereas the coupling ratio between sodium and taurine was at least three. In its cation dependence hypotaurine uptake thus resembled more GABA uptake than taurine uptake.