Proteoglycan synthesis in the intervertebral disc nucleus: the role
of extracellular osmolality.
Ishihara, Hirokazu, Katarina Warensjo, Sally Roberts, Jill P. G.
Urban.
University Laboratory of Physiology, Oxford University, Oxford OX1
3PT and Spinal Studies Centre, Roberts Jones and Agnes Hunt
Orthopaedic Hospital Trust, Oswestry, Shropshire, SY10, Dept
Orthopaedic Surgery, Toyama Medical and Pharmaceutical University,
Toyama, Japan
APStracts 3:0414C, 1996.
Proteoglycans, through their polyelectrolyte properties, regulate the
ionic composition and hence the osmotic pressure of the extracellular
matrix. We measured the change in 35S-sulphate incorporation, a
marker of proteoglycan synthesis, in explants of bovine nucleus
pulposus. During incubation, nucleus slices swelled 200 percent and
proteoglycans leached from the matrix, so that extracellular
osmolality fell from 420-450 mOsm to around 300 mOsm. When in vivo
extracellular osmolality was maintained either by adding 80 mM NaCl
or 150 mM sucrose to the swollen tissue, or by preventing swelling,
synthesis rates were 260-280% greater than in swollen tissue.
Synthesis rates also increased 200 percent in cells isolated from the
nucleus pulposus by enzyme digestion when medium osmolality was
raised from 280 to 430 mOsm by sucrose addition. The cells, either in
the tissue or isolated from it, swelled by more than 20% as
osmolality fell from 430 to 280 mOsm and showed little regulatory
volume decrease over 150 minutes. Synthesis rates thus appear to be
regulated by extracellular osmolality rather than by macromolecular
composition of the matrix and correlated well with measured changes
in cell volume.
Received 29 May 1996; accepted in final form 13 December 1996.
APS Manuscript Number C297-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996