Na + ‐Dependent Uptake and Release of Taurine by Neuroblastoma × Glioma Hybrid Cells

In neuroblastoma × glioma hybrid cells, a cell line of neuronal character, a saturable uptake system for taurine is found which displays high affinity and high capacity ( K m = 38 μ m , V = 1.25 nmol mg −1 min −1 )‐ Only the closely related structural analogues hypotaurine and β‐alanine are able to inhibit the transport of radioactively labeled taurine. Imipramine or haloperidol at 100 μ m effectively blocks taurine uptake. High‐affinity taurine uptake shows an absolute and highly specific requirement for Na + . The hybrid cells internalize taurine very slowly and, with 1 m m extracellular taurine, attain a plateau only after more than 20 h, at which time approximately 34 m m labeled taurine has accumulated in the cytosol. Generally there is hardly any spontaneous release of accumulated taurine. Efflux can, however, be induced by increasing the intracellular Na + content and is then accelerated by lowering the extracellular Na + concentration. The hypothesis is forwarded that taurine may exert its function by driving the extrusion of Na + in emergency situations.