<p>This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.</p> <p>Phosphotyrosine phosphatase (PTPase) activity and its regulation
by overnight food deprivation were studied in <italic>Psammomys
obesus</italic> (sand rat), a gerbil model of insulin resistance and nutritionally
induced diabetes mellitus. PTPase activity was measured
using a phosphopeptide substrate containing a sequence identical
to that of the major site of insulin receptor (IR) β-subunit autophosphorylation.
The PTPase activity in membrane fractions was 3.5-,
8.3-, and 5.9-fold lower in liver, fat, and skeletal muscle, respectively,
compared with corresponding tissues of albino rat.Western
blotting of tissue membrane fractions in <italic>Psammomys</italic> showed lower
PTPase and IR than in albino rats. The density of PTPase transmembrane
protein band was 5.5-fold lower in liver and 12-fold
lower in adipose tissue. Leukocyte antigen receptor (LAR) and IR
were determined by specific immunoblotting and protein bands
densitometry and were also found to be 6.3-fold lower in the liver
and 22-fold lower in the adipose tissue in the hepatic membrane
fractions. Liver cytosolic PTPase activity after an overnight food
deprivation in the nondiabetic <italic>Psammomys</italic>  rose 3.7-fold compared
with postprandial PTPase activity, but it did not change significantly
in diabetic fasted animals. Similar fasting-related changes
were detected in the activity of PTPase derived from membrane
fraction. In conclusion, the above data demonstrate that despite
the insulin resistance, <italic>Psammomys</italic>  is characterized by low level of
PTPase activities in membrane and cytosolic fractions in all 3 major insulin responsive tissues, as well as in liver. PTPase activity does
not rise in activity as a result of insulin resistance and nutritionally
induced diabetes.</p>
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Int J Exp Diabetes Res. 2002; 3(3):199-204