GLUT3 protein and mRNA in autopsy muscle specimens

GLUT3 is expressed in rat muscle, but this glucose transporter protein has not been identified previously in adult human skeletal muscle. We quantifie d the rapidity of disappearance of mRNA and protein from human skeletal mus cle at room temperature and at 4 degrees C. Fifty percent of the immunologi cally detectable GLUT3 protein disappeared by 1 hour at 20 degrees C and by 2 hours at 4 degrees C. mRNA for GLUT3 was decreased 50% by 2.2 hours at 2 0 degrees C and by 24 hours at 4 degrees C. Half of the measurable mRNAs fo r GLUT4, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), alpha-actin, and beta-myosin disappeared by 0.8 to 2.1 hours at 20 degrees C and by 5.0 to 16.6 hours at 4 degrees C. Previous conclusions that GLUT3 is not expressed in human muscle were likely drawn because of artifacts related to degradat ion of GLUT3 protein in the specimens prior to study. Because of the rapid degradation of protein and mRNA, autopsy specimens of muscle must be obtain ed within 6 hours of death, and even then, protein and mRNA data will likel y dramatically underestimate their expression in fresh muscle. Some previou sly published conclusions and recommendations regarding autopsy specimens a re not stringent enough to consistently yield useful protein and mRNA. Copy right (C) 1999 by W.B. Saunders Company.