Expression of rat ileal Na(+)-sulphate cotransport in Xenopus laevis oocytes: functional characterization.
Small-intestinal sulphate absorption is a Na(+)-dependent process having its highest rate in the ileum; it involves brush-border membrane Na(+)-sulphate cotransport. Injection of rat ileal mRNA into Xenopus laevis oocytes induced Na(+)-dependent sulphate uptake in a dose-dependent manner, with no apparent effect on Na(+)-independent sulphate uptake. For mRNA-induced transport, the apparent Km value for sulphate interaction was 0.6 +/- 0.2 mM and that for sodium interaction was 25 +/- 2 mM (Hill coefficient: 2.3 +/- 0.3). mRNA-induced transport, was inhibited by thiosulphate, but not by phosphate or 4,4,'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS). Using a rat renal Na(+)-sulphate cotransporter cDNA as a probe [NaSi-1; Markovich et al. (1993) Proc Natl Acad Sci USA 90:8073-8077], the highest hybridization signals (2.3 kb and 2.9 kb) were obtained in size fractions showing the highest expression of Na(+)-dependent sulphate transport in oocytes. Hybrid depletion experiments using antisense oligonucleotides (from the NaSi-1 cDNA sequence), provided further evidence that rat small-intestinal (ileal) Na(+)-sulphate cotransport is closely related to rat proximal-tubular brush-border membrane Na(+)-sulphate cotransport.
Perego
C
C
Institute of Physiology, University of Zürich, Switzerland.
Markovich
D
D
Norbis
F
F
Verri
T
T
Sorribas
V
V
Murer
H
H
D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D027682:Cation Transport Proteins; D018076:DNA, Complementary; D007082:Ileum / Q000378:metabolism*; D066298:In Vitro Techniques; D017136:Ion Transport / Q000502:physiology; D008969:Molecular Sequence Data; D016376:Oligonucleotides, Antisense; D009865:Oocytes / Q000378:metabolism; D012333:RNA, Messenger; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D000077003:Sodium Sulfate Cotransporter; D013431:Sulfates / Q000378:metabolism*; D027981:Symporters; D014982:Xenopus laevis
D002352:Carrier Proteins; D027682:Cation Transport Proteins; D018076:DNA, Complementary; D016376:Oligonucleotides, Antisense; D012333:RNA, Messenger; D000077003:Sodium Sulfate Cotransporter; D013431:Sulfates; D027981:Symporters; D012964:Sodium