AJP - Cell Physiology, Vol 257, Issue 4 C795-C801, Copyright © 1989 by American Physiological Society
Osmoregulation of glycerophosphorylcholine content of mammalian renal cells
T. Nakanishi and M. B. Burg
Laboratory of Kidney and Electrolyte Metabolism, National Heart, Lung, and Blood Institute, Bethesda, Maryland 20892.
Renal medullary cells contain high concentrations of "compatible" organic
osmolytes such as glycerophosphorylcholine (GPC), betaine, myo-inositol,
and sorbitol. The organic osmolytes occur as an osmoregulatory response to
the high and variable interstitial NaCl concentration that is part of the
urinary concentrating mechanism. Madin-Darby canine kidney (MDCK) cells in
culture were previously shown to accumulate GPC in response to increased
osmolality. We demonstrate here that this accumulation occurs in response
to elevated extracellular urea concentration as well as to elevated NaCl.
GPC does not accumulate unless either choline or GPC is present in the
medium. Thus the accumulation results from osmoregulated synthesis of GPC
from choline and, possibly, also osmoregulated uptake of extracellular GPC.
When the osmolality is decreased from high to normal levels, cell GPC
concentration decreases greatly over 24 h, accompanied by efflux of GPC and
choline into the medium.
