IDENTIFICATION OF A HIGH-AFFINITY TAURINE TRANSPORTER WHICH IS NOT DEPENDENT ON CHLORIDE

Taurine transport by lactating gerbil mammary tissue has been examined. Taurine uptake is mediated by a high-affinity system which is specific for beta-amino acids. The uptake of taurine is Na+-dependent but appears not to be obligatorly dependent upon Cl-. Thus, replacing Na+ with choline almost abolished taurine uptake. Substituting Cl- with NO3- had no effect whereas SCN- induced a small but significant increase in taurine influx. Taurine uptake was Na+-dependent under conditions where Cl- had been replaced with NO3-. However, it is apparent that the Na+-dependent taurine transport system requires the presence of a permeable anion because replacing Cl- with gluconate markedly reduced taurine uptake. Cell-swelling, induced by a hyposmotic challenge, increased the efflux of taurine from gerbil mammary tissue via a pathway sensitive to niflumic acid.