Expression of rabbit ileal N3 Na+/nucleoside cotransport activity in Xenopus laevis oocytes.
To determine if the Na+/nucleoside cotransport activity in the distal rabbit intestine has either purine-selective (N1) or broad (N3) substrate specificity, Na(+)-dependent inosine uptake was expressed in Xenopus laevis oocytes. The rate of expressed Na(+)-stimulated inosine uptake saturated with increasing inosine concentration (apparent K(m) = 58.2 +/- 13.0 microM), was insensitive to inhibition by 6-(4-nitrobenzyl)thio-9-beta-D-ribofuranosylpurine, and was partially inhibited by phloridzin. Na(+)-dependent uptake was inhibited by guanosine (IC50 = 7.1 microM) and thymidine (IC50 = 5.5 microM). The Na+/nucleoside cotransport activity expressed by rabbit ileal mRNA in the Xenopus oocyte expression system is most characteristic of the N3 subclass of this family of transport proteins.
Redlak
M J
MJ
Department of Internal Medicine, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298, USA.
Zehner
Z E
ZE
Betcher
S L
SL
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000502:physiology; D005260:Female; D006151:Guanosine / Q000494:pharmacology; D007082:Ileum; D007288:Inosine / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000378:metabolism*; D009865:Oocytes / Q000502:physiology*; D010695:Phlorhizin / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D011817:Rabbits; D012964:Sodium / Q000494:pharmacology; D027981:Symporters; D013872:Thionucleosides / Q000494:pharmacology; D013936:Thymidine / Q000494:pharmacology; D014982:Xenopus laevis
D002352:Carrier Proteins; D012333:RNA, Messenger; D027981:Symporters; D013872:Thionucleosides; D006151:Guanosine; C073034:sodium-nucleoside cotransporter; D007288:Inosine; D012964:Sodium; D010695:Phlorhizin; D013936:Thymidine