Regulation of na/myo-inositol cotransporter mrna levels and myo
-inositol uptake by osmolarity in cultured endothelial and neural
cells.
Wiese, Thomas J., Joyce A. Dunlap, Corinne E. Conner, John A.
Grzybowski, William L. Lowe, Jr, and Mark A. Yorek.
Department of Internal Medicine, Diabetes-Endocrinology Research
Center and Veterans Affairs Medical Center, University of Iowa, Iowa
City, IA 52246, Department of Medicine, Veterans Affairs Lakeside
Medical Center, and Northwestern University Medical School, Chicago,
IL 60611
APStracts 2:0356C, 1995.
myo-Inositol (MI) is an important factor in the synthesis of
phosphoinositides and, as an osmolyte, MI contributes to the
regulation of cell volume. In cells of renal origin, hypertonicity
causes an increase in Na/myo-inositol cotransporter (SMIT) mRNA
levels and MI transport. However, it is unknown whether changes in
osmolarity regulate transport of MI in neural or endothelial cells.
In these studies, neural and endothelial cell were exposed to
hyperosmotic medium for up to 48 h, and the effect on MI transport
determined. Transport of MI was maximally increased by exposing the
cells to hyperosmotic medium for 24 h. Kinetic analysis of high
-affinity MI transport demonstrated an increase in the apparent Vmax
with no significant change in the apparent Km. The hyperosmotic
induction of MI transport was blocked by the addition of
cycloheximide, indicating a requirement for protein synthesis, and
was associated with increased levels of SMIT mRNA. In contrast to the
effect of hypertonicity, exposure of neural and endothelial cells to
hypotonic conditions caused a decrease in SMIT mRNA levels and MI
transport in endothelial cells. These studies demonstrate that in
extrarenal cell types, changes in osmolarity also regulate SMIT
activity and mRNA levels.
Received 28 June 1995; accepted in final form 27 September 1995.
APS Manuscript Number C388-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95