Eccentric contractions decrease glucose transporter transcription rate, mRNA, and protein in skeletal muscle

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Abstract
We have recently shown that eccentric contractions (ECs; forced lengthening of active muscle) elicit a delayed decrease in glucose transporter (GLUT-4) protein content in rat skeletal muscle and a decrease in subsequent contraction-stimulated glucose transport. Here, we investigate whether this decrease in total GLUT-4 protein after prior ECs is due to changes in GLUT-4 gene transcription rate and GLUT-4 mRNA level. Furthermore, the effect of prior ECs on sarcolemmal GLUT-4 protein content in plasma membrane (PM) vesicles isolated from contraction-stimulated muscle was determined. Rat gastrocnemius muscle was electrically stimulated for ECs, and the contralateral muscle served, as unstimulated control (UC). Two days later, the total GLUT-4 protein content was decreased by 50% (P < 0.05) and 32% (P < 0.05) in the white and red gastrocnemius muscle, respectively. Furthermore, the GLUT-4 mRNA concentration was decreased by 41% (P < 0.05) in both the white and red gastrocnemius muscle. Moreover, the GLUT-4 transcription rate, determined by nuclear run-on analysis, was decreased by 75% (P < 0.05) in mixed EC gastrocnemius muscle compared with UC muscle. PM vesicles were isolated from EC and UC muscle after 15 min of isometric contractions. The PM GLUT-4 protein content was reduced by 51% (P < 0.05) in EC muscle compared with UC muscle. In conclusion, 2 days after ECs, the GLUT-4 transcription rate, GLUT-4 mRNA, and GLUT-4 protein content were decreased in rat skeletal muscle. Moreover, the PM GLUT-4 protein content in contraction-stimulated muscle was decreased. We suggest that eccentric muscle contractions decrease muscle GLUT-4 transcription rate, resulting in a lower GLUT-4 protein content, which in turn decreases the number of GLUT-4 transporters translocated to the sarcolemma, ultimately leading to decreased contraction-induced muscle glucose transport.