Osmotic regulation of amino acids and system a transport in madin
-darby canine kidney cells.
Horio, Masaru, Atsushi Yamauchi, Toshiki Moriyama, Enyu Imai, and
Yoshimasa Orita.
Department of Clinical Laboratory Science,School of Allied Health
Science, Osaka University School of Medicine, First Department of
Medicine, Osaka University School of Medicine, Faculty of Health and
Sport Science, Osaka University School of Medicine, 2-2, Yamadaoka,
Suita, Osaka, 565, Japan
APStracts 3:0332C, 1996.
The effects of hypertonicity on the intracellular amino acid content
and system A transport activity have been studied in MDCK cells.
Total content of 20 amino acids increased from 274 to 689 nmol/mg
protein after 8 h of hypertonicity (500 mosmol/kg), remaining almost
constant until after 6 days of hypertonicity. The content of neutral
amino acids increased from 77 to 307 and 395 nmol/mg protein after 8
h and 6 days of hypertonicity, respectively, accounting for 73% of
the increased amount of total amino acids. In the hypertonic MDCK
cells, system A transport activity, measured by Na+-dependent 2
-methylamino-isobutyric acid (MeAIB) uptake, increased about 60-fold
the uptake in isotonic cells. MeAIB was taken up primarily on basal
side in the isotonic MDCK cells cultured on permeable supports.
Extracellular hypertonicity stimulated the MeAIB uptake on basal side
predominantly. These results indicated that amino acids, especially
neutral amino acids, can function as the volume regulating osmolytes
and the stimulation of system A activity appears to contribute to the
accumulation of the neutral amino acids in hypertonic MDCK cells.
Received 19 June 1996; accepted in final form 27 September 1996.
APS Manuscript Number C351-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 November 1996