Protein Tyrosine Phosphatase Activity in Insulin-Resistant Rodent Psammomys ObesusReport as inadecuate

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International Journal of Experimental Diabetes Research - Volume 3 2002, Issue 3, Pages 199-204

Pediatric Division, Chaim Sheba Medical Center, Tel-Hashomer, Israel

Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel

Diabetes Research Unit and Department of Biochemistry, Hadassah-Hebrew University Medical Center, Jerusalem 91120, Israel

Received 28 February 2002; Accepted 12 May 2002

Copyright © 2002 Hindawi Publishing Corporation. 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.


Phosphotyrosine phosphatase PTPase activity and its regulationby overnight food deprivation were studied in Psammomysobesus sand rat, a gerbil model of insulin resistance and nutritionallyinduced diabetes mellitus. PTPase activity was measuredusing a phosphopeptide substrate containing a sequence identicalto 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.Westernblotting of tissue membrane fractions in Psammomys showed lowerPTPase and IR than in albino rats. The density of PTPase transmembraneprotein band was 5.5-fold lower in liver and 12-foldlower in adipose tissue. Leukocyte antigen receptor LAR and IRwere determined by specific immunoblotting and protein bandsdensitometry and were also found to be 6.3-fold lower in the liverand 22-fold lower in the adipose tissue in the hepatic membranefractions. Liver cytosolic PTPase activity after an overnight fooddeprivation in the nondiabetic Psammomys rose 3.7-fold comparedwith postprandial PTPase activity, but it did not change significantlyin diabetic fasted animals. Similar fasting-related changeswere detected in the activity of PTPase derived from membranefraction. In conclusion, the above data demonstrate that despitethe insulin resistance, Psammomys is characterized by low level ofPTPase activities in membrane and cytosolic fractions in all 3 major insulin responsive tissues, as well as in liver. PTPase activity doesnot rise in activity as a result of insulin resistance and nutritionallyinduced diabetes.

Author: Joseph Meyerovitch, Yigal Balta, Ehud Ziv, Joseph Sack, and Eleazar Shafrir



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