Effect of Osmolality and myo-Inositol Deprivation on the Transport Properties of myo-Inositol in Primary Astrocyte Cultures |
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Authors: | Isaacks R E Bender A S Kim C Y Norenberg M D |
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Institution: | (1) Research Laboratories, Veterans Affairs Medical Center, Miami, Florida;(2) Department of Medicine, University of Miami School of Medicine, Miami, Florida, 33125;(3) Department of Pathology, University of Miami School of Medicine, Miami, Florida, 33125;(4) Research Service (151), Veterans Affairs Medical Center, Miami, Florida, 33125 |
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Abstract: | myo-Inositol uptake measured in primary astrocyte cultures was saturable in the presence of Na+ with a Km of 13–18 M and a Vmax of 9.4 nmoles/mg protein/hour in myo-inositol-fed cells, indicating a high affinity transport system. In myo-inositol-deprived cells, Km was about 53 M with a Vmax of 13.2 nmoles/mg protein/hour. Decreasing osmolality decreased the Vmax to about 1.9 nmoles/mg protein/hour whereas increasing osmolality increased Vmax about 5-fold, while Kms were essentially unchanged in myo-inositol fed cells. In cells deprived of myo-inositol, Vmax decreased in hypotonic medium and increased in hypertonic medium almost 10-fold, but with more than a doubling of the Km regardless of the osmolality. Glucose (25 mM) inhibited myo-inositol uptake 51% whereas the other hexoses used inhibited uptake much less. Our findings indicate that myo-inositol uptake in astrocytes occurs through an efficient carrier-mediated Na+-dependent co-transport system that is different from that of glucose and its kinetic properties are affected by myo-inositol availability and osmotic stress. |
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Keywords: | myo-Inositol astrocytes osmolality deprivation kinetic parameters |
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