Taurine and hypotaurine transport in neuroblastoma cells: effects of cations.
The cation requirements of [(3)H]taurine and [(35)S]hypotaurine uptake by cultured neuroblastoma C1300 cells were compared in Krebs-Ringer-Hepes-glucose medium. The uptakes were strictly sodium-dependent at both low and high taurine and hypotaurine concentrations. The omission of Ca(2+) or Mg(2+) ions affected uptakes only marginally. The optimal K(+) concentration was equal to the physiological concentration, whereas abnormally high K(+) levels inhibited similarly taurine and hypotaurine uptake. The sodium dependence curves of both uptakes were sigmoidal in character at low and high taurine and hypotaurine concentrations. Hill plots suggest that two Na(+) ions are coupled with the transfer of one taurine or hypotaurine molecule into neuroblastoma cells. With respect to cation requirements taurine and hypotaurine transports are similar in cultured neuroblastoma cells and display features considered typical of the uptake of a neurotransmitter amino acid.