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1 Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA, USA
2 Department of Biochemistry and Molecular Biology, The Pennsylvania State University College of Medicine, Hershey, PA, USA
* To whom correspondence should be addressed. E-mail: rkeil{at}psu.edu.
Volatile anesthetics are essential for modern medical practice but sites and mechanisms of action for any of their numerous cellular effects remain largely unknown. Previous studies with yeast showed volatile anesthetics induce nutrient-dependent inhibition of growth through mechanisms involving inhibition of mRNA translation. Studies herein show that the volatile anesthetic halothane inhibits protein synthesis in perfused rat liver at doses ranging from 2% to 6%. A marked disaggregation of polysomes occurs indicating inhibition of translation initiation plays a key role. Dose- and time-dependent alterations that decrease the function of a variety of translation initiation processes are observed. At 6% halothane, a rapid and persistent increase in phosphorylation of the
-subunit of eukaryotic translation initiation factor (eIF) -2 occurs. This is accompanied by inhibition of activity of the guanine-nucleotide exchange factor eIF2B responsible for GDP/GTP exchange on eIF2. At lower doses, neither eIF2
phosphorylation nor eIF2B activity is altered. After extended exposure to 6% halothane, alterations in two separate responses regulated by the target-of-rapamycin pathway occur: 1) redistribution of eIF4E from its translation-stimulatory association with eIF4G to its translation-inactive complex with eIF4E binding protein 1 (4E-BP1); and 2) decreased phosphorylation of ribosomal protein S6 (rpS6) with a corresponding decrease in active forms of a kinase that phosphorylates rpS6 (p70S6K1). Only changes in the association of eIF4E and eIF4G are observed after extended exposure to low anesthetic doses. Thus, dose- and time-dependent alterations in multiple processes permit liver cells to adapt translation to variable degrees and duration of stress imposed by anesthetic exposure.
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