EXPRESSION OF RAT RENAL SULFATE TRANSPORT-SYSTEMS IN XENOPUS-LAEVIS OOCYTES - FUNCTIONAL-CHARACTERIZATION AND MOLECULAR-IDENTIFICATION

Renal proximal tubular sulfate reabsorption is mediated by brush borde r membrane Na+/sulfate-cotransport and basolateral Na+-independent sul fate transport. Injection of rat kidney cortex mRNA into Xenopus laevi s oocytes induced Na+-dependent as well as Na+-independent sulfate tra nsport. The inhibition pattern of Na+-dependent uptake coincided with that known for the brush border membrane; the inhibition pattern of Na +-independent uptake suggested that this activity could be related to the basolateral cell surface. By Northern blot hybridization of size-f ractionated mRNA, we provide evidence that the Na+-dependent uptake is induced by an mRNA species related to a recently cloned cDNA encoding rat renal cortex Na+/SO4 Cotransport (NaSi-1; Markovich, D., Forgo, J ., Stange, G., Biber, J., and Murer, H. (1993) Proc. Natl. Acad. Sci. U. S. A. 90,8073-8077); the Na+-independent sulfate transport activity seems to be related to an mRNA species encoding a rat liver Na+-indep endent sulfate transporter (Bissig, M., Hagenbuch, B., Stieger, B., Ko ller, T., and Meier, P. J. (1994) J. Biol. Chem. 269,3017-3021). Hybri d depletion experiments using antisense oligonucleotides provided furt her evidence for the association of the expressed transport activities to NaSi-1 and sat-1, respectively.