Effect of osmolality and myo-inositol deprivation on the transport properties of myo-inositol in primary astrocyte cultures.
myo-Inositol uptake measured in primary astrocyte cultures was saturable in the presence of Na+ with a Km of 13-18 microM 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 microM 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.
Isaacks
R E
RE
Research Laboratories, Veterans Affairs Medical Center, Miami, Florida 33125, USA.
Bender
A S
AS
Kim
C Y
CY
Norenberg
M D
MD
D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D001693:Biological Transport, Active / Q000187:drug effects; D002478:Cells, Cultured; D006601:Hexoses / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007294:Inositol / Q000172:deficiency* / Q000378:metabolism / Q000502:physiology; D007700:Kinetics; D009994:Osmolar Concentration; D009997:Osmotic Pressure; D051381:Rats; D012964:Sodium / Q000494:pharmacology; D013997:Time Factors
D006601:Hexoses; D007294:Inositol; D012964:Sodium