myo-Inositol binding and transport in brush border membranes of rat kidney |
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Authors: | Tadaomi Takenawa Eiko Wada Toru Tsumita |
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Institution: | Department of Cell Chemistry, Institute of Medical Science, The University of Tokyo, Takanawa 108, Tokyo and Institute of Basic Medicine, University of Tsukuba, Niiharu, Ibaragi Japan |
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Abstract: | Using hypotonically treated brush border membranes, binding and transport of myo-inositol were examined.By hypotonic treatment, both total and non-specific uptake decreased significantly, but specific uptake was not affected.myo-Inositol release from membranes preloaded by incubation for 2 min was very rapid and about 98% of preloaded myo-inositol was released in 5 min of incubation. However, myo-inositol release from membranes preloaded by incubation for 20 min was fairly slow and 50% of myo-inositol remained in the membranes even after 10 min of incubation.Uptake of myo-inositol decreased by the increase of osmolarity in the medium. However, effect of osmolarity on the uptake was less significant when myo-inositol concentration was lower.Under conditions in which mainly binding occurred, myo-inositol binding to the membranes was measured. Two binding systems were demonstrated and high affinity site could bind 22 pmol/mg protein at most and the apparent value was 8.3 μM.Both binding and transport processes were dependent on Na+ and enhanced by Na+-gradient. |
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