Disturbed Ca2+ kinetics in N-deacetylase/N-sulfotransferase-1 defective myotubes.
2003
The biosynthesis of heparan sulfate, present on the cell surface and in the
basal lamina surrounding cells, is a multistep process in which each step is
mediated by a specific enzyme. The initial modification of the precursor
polysaccharide, N -deacetylation followed by N -sulfation of
selected N -acetyl-D-glucosamine residues, is catalyzed by the enzyme
glucosaminyl N -deacetylase/ N -sulfotransferase (NDST). This
event is a key step that regulates the overall sulfate content of the
polysaccharide. Here, we report on the effects of NDST deficiency on
Ca 2+ kinetics in myotubes from NDST-1- and NDST-2-deficient mice,
indicating a novel role for heparan sulfate in skeletal muscle physiology. Immunostaining for specific heparan sulfate epitopes showed major changes
in the heparan sulfate composition in skeletal muscle tissue derived from
NDST-1 –/– mice and NDST –/–
cultured myotubes. Biochemical analysis indicates a relative decrease in both
N -sulfation and 2- O -sulfation of skeletal muscle heparan
sulfate. The core protein of heparan sulfate proteoglycan perlecan was not
affected, as judged by immunohistochemistry. Also, acetylcholine receptor
clustering and the occurrence of other ion channels involved in
excitation-contraction coupling were not altered. In
NDST-2 –/– mice and heterozygous mice no changes in
heparan sulfate composition were observed. Using high-speed UV confocal laser
scanning microscopy, aberrant Ca 2+ kinetics were observed in
NDST-1 –/– myotubes, but not in
NDST-2 –/– or heterozygous myotubes. Electrically
induced Ca 2+ spikes had significantly lower amplitudes, and a
reduced removal rate of cytosolic Ca 2+ , indicating the importance
of heparan sulfate in muscle Ca 2+ kinetics.
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