Cloning and functional expression of an SGLT-1-like protein from the Xenopus laevis intestine

Katsumi Nagata, Naohiro Hori, Kenzo Sato, Kunimasa Ohta, Hideaki Tanaka, Yasutake Hiji

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Abstract

A cDNA encoding an Na+-glucose cotransporter type 1 (SGLT-1)-like protein was cloned from the Xenopus laevis intestine by the 5'- and 3'-rapid amplification of cDNA ends method. The deduced amino acid sequence was 673 residues long, with a predicted mass of 74.1 kDa and 52-53% identity to mammalian SGLT-1s. This gene was expressed in the small intestine and kidney, reflecting a tissue distribution similar to that of SGLT-1. The function of the protein was studied using the two-microelectrode voltage-clamp technique after injection of cRNA into Xenopus laevis oocytes. Perfusion with myo- inositol elicited about twofold larger inward currents than perfusion with D- glucose. The order of the substrate specificity was myoinositol > D-glucose > D-galactose ≥ α-methyl-D-glucoside. The current induced by myo-inositol increased with membrane hyperpolarization and depended on external myoinositol and Na+: the apparent Michaelis-Menten constant was 0.25 ± 0.07 (SD) mM with myo-inositol, whereas the apparent concentration for half- maximal activation was 12.5 ± 1.0 mM and the Hill coefficient was 1.6 ± 0.1 with Na+. In conclusion, the cloned protein shares features with both SGLT- 1 and the Na+-myo-inositol cotransporter.

Original languageEnglish
Pages (from-to)G1251-G1259
JournalAmerican Journal of Physiology - Gastrointestinal and Liver Physiology
Volume276
Issue number5 39-5
Publication statusPublished - May 1 1999
Externally publishedYes

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All Science Journal Classification (ASJC) codes

  • Physiology
  • Hepatology
  • Gastroenterology
  • Physiology (medical)

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