Effect of ammonia and methionine sulfoximine on myoinositol transport in cultured astrocytes

Russell E. Isaacks, Alexander S. Bender, Chang Y. Kim, You F. Shi, Michael D. Norenberg

Research output: Contribution to journalArticle

23 Scopus citations

Abstract

Ammonia causes astrocyte swelling which is abrogated by methionine sulfoximine (MSO). Since myo-inositol is an important osmolyte, we investigated the effects of ammonia and MSO on myoinositol flux in cultured astrocytes for periods up to 72 hours. Uptake of myo-inositol was significantly decreased by 26.7 (P < 0.05) and 39.3 (P < 0.006) percent after 48 hours of exposure to 5 or 10 mM ammonia, respectively. The maximum rate of uptake was 14.0 ± 0.5 nmol/hour/mg protein which was reduced to 7.45 ± 0.27 and 7.02 ± 0.57 nmoles/hour/mg protein by 5 or 10 mM ammonia, respectively. The Kms by Michaelis-Menten equation for the control, and in the presence of 5, or 10 mM ammonia were 32.5 ± 4.52, 44.4 ± 5.82, and 39.3 ± 7.0 μM, respectively. Kms by Hanes-Woolf plot for the control, 5, or 10 mM ammonia were 25, 45, and 40 μM, respectively. Treatment of astrocytes with either 5 or 10 mM NH4Cl for 6 hours caused a decrease in myo-inositol content by 66% and 58%, respectively. MSO (3 mM) partially diminished the ammonia-induced inhibition of myo-inositol uptake and decreased myo-inositol content by 31% after 24 hours. Additionally, ammonia increased myo-inositol efflux briefly through the fast efflux component but had little effect on myo-inositol efflux through the slow efflux component of astrocytes exposed to ammonia for up to 72 hours. Predominantly decreased myo-inositol influx coupled with brief efflux through the fast component may represent an adaptive response to diminish the extent of ammonia-induced astrocyte swelling.

Original languageEnglish (US)
Pages (from-to)51-59
Number of pages9
JournalNeurochemical Research
Volume24
Issue number1
DOIs
StatePublished - Feb 13 1999

Keywords

  • Ammonia
  • Astrocytes
  • Cell swelling
  • Hepatic encephalopathy
  • Methionine sulfoximine
  • Myoinositol transport

ASJC Scopus subject areas

  • Neuroscience(all)
  • Biochemistry

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