The effect of glucose and galactose toxicity on myo-inositol transport and metabolism in human skin fibroblasts in culture.
Myo-inositol transport and metabolism were studied in cultured human skin fibroblasts exposed to potentially toxic levels of glucose or galactose. Although variable among 11 different cell lines, the myo-inositol level in confluent cells, ranging from 10-50 nmol/mg protein, was constant with passage. A high-affinity transport system for myo-inositol had an apparent Kt of 55 microM and Vmax of 16 pmol/min/mg protein. No obvious relationship existed between cellular levels and transport capacity. Dependency on sodium was complex. When medium sodium was lowered to 23 mM, myo-inositol uptake ceased after about 1 h. However, the initial rate of myo-inositol uptake only showed a sodium dependence at low myo-inositol concentrations. Both phloretin and phloridzin inhibited myo-inositol uptake. Phloridzin had a Ki of 60 microM, and phloretin was either a noncompetitive or uncompetitive inhibitor. Glucose and galactose were only weak competitive inhibitors, with a Ki of 30 mM and 65 mM, respectively. After 24 h of incubation with myo-[2-3H]inositol, only 10% of the total cell label was incorporated into phospholipid. Compared with control media with 5 mM glucose, the incubation of confluent cells in media with 20 mM glucose had little effect on intracellular glucose and sorbitol, whereas cells incubated in control media supplemented with 5 mM galactose showed a large increase in galactose and polyol levels. In media with more than 200 microM of myo-inositol, neither treatment had an effect on myo-inositol levels after 24 h.(ABSTRACT TRUNCATED AT 250 WORDS)
Berry
G T
GT
Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia 19104.
Prantner
J E
JE
States
B
B
Yandrasitz
J R
JR
D001693:Biological Transport, Active / Q000187:drug effects; D002460:Cell Line; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D005690:Galactose / Q000633:toxicity*; D005947:Glucose / Q000633:toxicity*; D006801:Humans; D007294:Inositol / Q000378:metabolism / Q000493:pharmacokinetics*; D007700:Kinetics; D010693:Phloretin / Q000494:pharmacology; D010695:Phlorhizin / Q000494:pharmacology; D012867:Skin / Q000187:drug effects / Q000378:metabolism; D012964:Sodium / Q000494:pharmacology
D007294:Inositol; D012964:Sodium; D010695:Phlorhizin; D005947:Glucose; D010693:Phloretin; D005690:Galactose