Kinetic evidence for compartmentalization of myo-inositol in hepatocytes

Samuel H. Sigal, John R. Yandrasitz, Gerard T. Berry

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

myo-Inositol uptake and conversion to phosphatidylinositol (PI) was studied in isolated rat hepatocytes. Uptake of myo-[2-3H]-inositol into the trichloroacetic acid (TCA)-soluble fraction showed no evidence of saturation, while incorporation into lipid had an apparent Km of 0.28 mmol/L for external myo-inositol. With 50 μmol/L myo-[2-3H]-inositol, approximately half of the radiolabel was found in lipid at 30 minutes. Glucose and galactose were weak inhibitors, while phlorizin at 1 mmol/L reduced uptake by 50%. Metabolic inhibitors reduced incorporation of myo-[2-3H]-inositol into lipid, but had no effect on uptake. Hepatocytes maintained myo-inositol levels of 0.4 mmol/L for 60 minutes when incubated with 50 μmol/L myo-inositol, but levels increased when incubated with 1 mmol/L myo-inositol. Efflux of label was studied in hepatocytes prelabeled for 20 minutes with myo-[2-3H]-inositol. Loss of label was initially rapid, but had slowed by 20 minutes, with much of the label remaining in the cells. Phlorizin inhibited the loss of myo-[2-3H]-inositol, while increasing myo-inositol concentration in the medium enhanced efflux. The effects of these agents on the rate of efflux was found in lipid rather than in the TCA-soluble myo-inositol fraction. These findings suggest that myo-inositol is compartmentalized within hepatocytes, with a bulk metabolically inert pool and a smaller active pool that equilibrates with extracellular myo-inositol via an energy-independent carrier-mediated mechanism, and is preferentially available for efflux or for synthesis of phosphoinositides.

Original languageEnglish (US)
Pages (from-to)395-401
Number of pages7
JournalMetabolism
Volume42
Issue number3
DOIs
StatePublished - 1993
Externally publishedYes

Fingerprint

Inositol
Hepatocytes
Phlorhizin
Lipids
Trichloroacetic Acid
Phosphatidylinositols
Galactose

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Endocrinology

Cite this

Kinetic evidence for compartmentalization of myo-inositol in hepatocytes. / Sigal, Samuel H.; Yandrasitz, John R.; Berry, Gerard T.

In: Metabolism, Vol. 42, No. 3, 1993, p. 395-401.

Research output: Contribution to journalArticle

Sigal, Samuel H. ; Yandrasitz, John R. ; Berry, Gerard T. / Kinetic evidence for compartmentalization of myo-inositol in hepatocytes. In: Metabolism. 1993 ; Vol. 42, No. 3. pp. 395-401.
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abstract = "myo-Inositol uptake and conversion to phosphatidylinositol (PI) was studied in isolated rat hepatocytes. Uptake of myo-[2-3H]-inositol into the trichloroacetic acid (TCA)-soluble fraction showed no evidence of saturation, while incorporation into lipid had an apparent Km of 0.28 mmol/L for external myo-inositol. With 50 μmol/L myo-[2-3H]-inositol, approximately half of the radiolabel was found in lipid at 30 minutes. Glucose and galactose were weak inhibitors, while phlorizin at 1 mmol/L reduced uptake by 50{\%}. Metabolic inhibitors reduced incorporation of myo-[2-3H]-inositol into lipid, but had no effect on uptake. Hepatocytes maintained myo-inositol levels of 0.4 mmol/L for 60 minutes when incubated with 50 μmol/L myo-inositol, but levels increased when incubated with 1 mmol/L myo-inositol. Efflux of label was studied in hepatocytes prelabeled for 20 minutes with myo-[2-3H]-inositol. Loss of label was initially rapid, but had slowed by 20 minutes, with much of the label remaining in the cells. Phlorizin inhibited the loss of myo-[2-3H]-inositol, while increasing myo-inositol concentration in the medium enhanced efflux. The effects of these agents on the rate of efflux was found in lipid rather than in the TCA-soluble myo-inositol fraction. These findings suggest that myo-inositol is compartmentalized within hepatocytes, with a bulk metabolically inert pool and a smaller active pool that equilibrates with extracellular myo-inositol via an energy-independent carrier-mediated mechanism, and is preferentially available for efflux or for synthesis of phosphoinositides.",
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