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J. Biol. Chem., Vol. 280, Issue 7, 5510-5515, February 18, 2005

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Effects of Insulin and Transgenic Overexpression of UDP-glucose Pyrophosphorylase on UDP-glucose and Glycogen Accumulation in Skeletal Muscle Fibers^*

Thomas H. Reynolds, IV, Yunbae Pak¶, Thurl E. Harris, Jill Manchester||, Eugene J. Barrett**, and John C. Lawrence, Jr.**

From the Departments of Pharmacology and ^**Medicine, University of Virginia School of Medicine, Charlottesville, Virginia 22908, the Department of Exercise and Sport Sciences, Ithaca College, Ithaca, New York 14850, the ^¶Department of Biochemistry, Gyeongsang National University, Jinju 666-701, Korea, and the ^||Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, Missouri 63110

UDP-glucose (UDP-Glc) and glycogen levels in skeletal muscle fibers of defined fiber type were measured using microanalytical methods. Infusing rats with insulin increased glycogen in both Type I and Type II fibers. Insulin was without effect on UDP-Glc in Type I fibers but decreased UDP-Glc by 35–40% in Type IIA/D and Type IIB fibers. The reduction in UDP-Glc suggested that UDP-Glc pyrophosphorylase (PPL) activity might limit glycogen synthesis in response to insulin. To explore this possibility, we generated mice overexpressing a UDP-Glc PPL transgene in skeletal muscle. The transgene increased both UDP-Glc PPL activity and levels of UDP-Glc in skeletal muscles by 3-fold. However, overexpression of UDP-Glc PPL was without effect on either the levels of skeletal muscle glycogen or glucose tolerance in vivo. The transgene was also without effect on either control or insulin-stimulated rates of ¹⁴C-glucose incorporation into glycogen in muscles incubated in vitro. The results indicate that UDP-Glc PPL activity is not limiting for glycogen synthesis.

Received for publication, December 3, 2004

^* This work was supported by National Institutes of Health Grant DK-28312. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

To whom correspondence should be addressed: Dept. of Pharmacology, P. O. Box 800735, 1300 Jefferson Park Ave., Charlottesville, VA 22908-0735. Tel.: 434-924-1584; Fax: 434-982-3575; E-mail: jcl3p{at}virginia.edu.

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