IONIC REQUIREMENTS OF PERITUBULAR TAURINE TRANSPORT IN FUNDULUS KIDNEY

A peritubular mechanism for active taurine uptake, simialr to that previously found in the flounder, was demonstrated in killifish (Fundulus heteroclitus) teased renal tubules. Other .beta.-amino acids and glycine inhibited taurine transport. Uptake exhibited a nearly absolute requirement for external Na+. The stoichiometric relationship between Na+ and taurine was found to be 2:1. Medium Cl- markedly stimulated the Na+-dependent taurine uptake, but none of the other small monovalent anions tested .**GRAPHIC**. Br-, SCN-) could substitute for Cl- in activating taurine transport. Cl- replacement resulted in a significant decrease in Vmax, whereas the affinity of the carrier for taurine appeared to be unaffected. In the absence of Cl- the Na+ dependence of taurine influx was reduced to a stoichiometric relationship of 1.4 Na+:1 taurine, indicating an effect of Cl- on the binding of Na+ to the transport system. A model for Na+-Cl--taurine cotransport is presented.