Abstract
Renal proximal tubular sulfate reabsorption is mediated by brush border membrane Na+/sulfate-cotransport and basolateral Na(+)-independent sulfate transport. Injection of rat kidney cortex mRNA into Xenopus laevis oocytes induced Na(+)-dependent as well as Na(+)-independent sulfate transport. 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-fractionated 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(+)-independent sulfate transporter (Bissig, M., Hagenbuch, B., Stieger, B., Koller, T., and Meier, P. J. (1994) J. Biol. Chem. 269, 3017-3021). Hybrid depletion experiments using antisense oligonucleotides provided further evidence for the association of the expressed transport activities to NaSi-1 and sat-1, respectively.
Highlights
Renal proximal tubular sulfate reabsorptionis medi- Two cDNAs most likely involved in sulfate transport were atedby brush border membrane Na+/sulfate-cotransporretcently identified:a cDNA (Nasi-1) related torat renal cortex and basolateral Na+-independent sulfate transport
11 To whom correspondence should be addressed: Institute of Physiology, University of Ziirich, Winterthurerstrasse 190, CH-8057 Zurich, Isolation of RNA, mRNA, and Sucrose Fractionation-Kidney cortex tissue was extracted from male Sprague-Dawleyrats (180-200 9).Total RNA was extracted from rat kidney cortex according to the protocol described elsewhere [31, 32], and mRNA was isolated and size-fractionated by sucrosedensity gradient centrifugation as described earlier
In our experiments, weobserved expression of both Na+dependent and Na+-independentSO4transport inducedby rat kidney cortex mRNA injected into X.laevis oocytes
Summary
Renal proximal tubular sulfate reabsorptionis medi- Two cDNAs most likely involved in sulfate transport were atedby brush border membrane Na+/sulfate-cotransporretcently identified:a cDNA (Nasi-1) related torat renal cortex and basolateral Na+-independent sulfate transport. The injection of rat renal cortex mRNA intoX.Zaeuis oocytes gave rise to a saturablestimulation of sulfate transport,both in the presence and absence of Na+ (Fig. lA).This suggests the presence of two separate SO4transport systems: a Na+-dependent and a Na+-independent pathway.
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