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Kwon, H. Moo
Inflammation and Kidney Disorder Lab
Research Interests
  • TonEBP, Obesity, Cancer, Chronic inflammatory diseases, Brain disorder, Kidney disorders, Genomic instability

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Effect of extracellular pH on the myo-inositol transporter SMIT expressed in Xenopus oocytes

Cited 18 times inthomson ciCited 17 times inthomson ci
Title
Effect of extracellular pH on the myo-inositol transporter SMIT expressed in Xenopus oocytes
Author
Matskevitch, JWagner, CARisler, TKwon, H. MooHandler, JSWaldegger, SBusch, AELang, F
Keywords
acidosis; cell volume; inositol; Na+-coupled transport; osmolytes; SMIT
Issue Date
199811
Publisher
SPRINGER
Citation
PFLUGERS ARCHIV-EUROPEAN JOURNAL OF PHYSIOLOGY, v.436, no.6, pp.854 - 857
Abstract
The myo-inositol transporter SMIT is expressed particularly at high extracellular osmolarity and serves to accumulate the osmolyte myo-inositol. Transport of myo-inositol is coupled to the cotransport of Na+ and is electrogenic. In Xenopus oocytes injected with mRNA encoding SMIT but not in water-injected oocytes, myo-inositol creates an inward current that is dependent on the ambient Na+ concentration. The present study has been performed to elucidate the pH dependence of myo-inositol-induced currents. Therefore, Xenopus oocytes were injected with mRNA encoding SMIT and two-electrode voltage-clamp studies were performed. The myo-inositol-induced currents in oocytes expressing SMIT were found to have a sigmoidal dependence on the ambient pH between pH 5.5 and 8.5 with an apparent K-i of 0.21+/-001 mu M H+ and a Hill coefficient of 1.80+/-0.16. Kinetic analysis of the myo-inositol-induced currents at pH 8.0 and -90 mV holding potential revealed a Hill coefficient of 0.93+/0.07 and an apparent K-m, for myo-inositol of 0.031+/-0.003 mM as well as a Hill coefficient of 1.64+/-0.24 and an apparent K-m of 38.8+/-4.1 mM for Na+. A decrease of the Na+ concentration from 150 mM to 50 mM significantly altered the maximal observed current and increased the apparent K-m for myo-inositol. Acidification to pH 6.5 significantly increased the apparent K-m for myo-inositol and for Na+ to 0.057+/-0.005 mM and 73.9+/-4.8 mM, respectively. The Hill coefficients for myo-inositol and Na+ were not affected and remained close to 1 for myo-inositol and 2 for Na+. In summary, acidification impedes SMIT-mediated myo-inositol transport at least partially by decreasing the affinity of the carrier for Na+. The impaired Na+ binding subsequently decreases binding and transport of myo-inositol.
URI
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DOI
http://dx.doi.org/10.1007/s004240050714
ISSN
0031-6768
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