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Ascorbic acid accumulation and transport in human fibroblasts

R W Welch1, P Bergsten, J D Butler

  • 1Laboratory of Cell Biology and Genetics, National Institute of Diabetes, Digestive, and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892.

The Biochemical Journal
|September 1, 1993
PubMed
Summary

This study explored how human fibroblasts take up ascorbic acid, a form of vitamin C. Using a special detection method, researchers found that fibroblasts accumulate ascorbic acid up to 20 times higher than the surrounding environment. Two distinct transport systems were identified: one with high affinity and one with low affinity. The high-affinity system is similar to what's seen in neutrophils, but the low-affinity system in fibroblasts is different. Both systems were affected by inhibitors, suggesting they are active transport processes. The findings suggest that fibroblasts may be a useful model for studying how cells regulate ascorbic acid levels.

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Area of Science:

  • Cellular transport mechanisms in human physiology
  • Vitamin metabolism in human cells
  • Molecular pharmacology of ascorbic acid

Background:

Prior research has established that ascorbic acid is essential for various physiological functions, including collagen synthesis and antioxidant activity. However, the specific mechanisms by which human fibroblasts accumulate this vitamin remain unclear. While studies have explored ascorbic acid transport in neutrophils, fibroblasts have not been systematically examined in this context. This gap motivated the investigation of transport kinetics in fibroblasts to determine whether similar or distinct mechanisms apply. It was already known that transporters mediate ascorbic acid uptake in some cell types, but the role of these transporters in fibroblasts had not been resolved. No prior work had resolved whether fibroblasts use a single or multiple transport systems for ascorbic acid. The absence of data on fibroblast-specific transport mechanisms left uncertainty about how these cells regulate vitamin C levels. This uncertainty drove the current study to characterize transport activity and identify potential transporters involved.

Keywords:
ascorbic acidhuman fibroblaststransport mechanismsvitamin C kinetics

Frequently Asked Questions

The study identified a high-affinity transporter with a Km of 6 microM and a low-affinity transporter with a Km of 5 mM.

Accumulation was measured using high-performance liquid chromatography with coulometric electrochemical detection.

The low-affinity transporter was inhibited by specific transport inhibitors, indicating it is not passive diffusion.

The high-affinity transporter in fibroblasts is similar to that in neutrophils, with comparable Km and Vmax values.

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Purpose Of The Study:

The aim of this study was to investigate ascorbic acid accumulation in human fibroblasts for the first time. Researchers sought to determine whether fibroblasts use active transport mechanisms to accumulate ascorbic acid against a concentration gradient. The specific problem addressed was the lack of information on fibroblast-specific transport systems for this vitamin. The motivation stemmed from the need to understand how fibroblasts regulate intracellular ascorbic acid levels. By examining transport kinetics, the study aimed to identify whether multiple transport activities are involved. The researchers proposed that fibroblasts may employ a two-component transport system, as previously observed in neutrophils. This study aimed to confirm or refute that hypothesis in a new cell type. The findings could clarify whether such transport mechanisms are generalized across human cell types.

Main Methods:

The study used high-performance liquid chromatography with coulometric electrochemical detection to measure ascorbic acid accumulation in fibroblasts. Researchers exposed fibroblasts to varying concentrations of ascorbic acid and measured uptake rates. Metabolic inhibitors were applied to assess the role of energy-dependent transport. Inhibitors specific to ascorbic acid transport in neutrophils were also tested. The transport activity was analyzed using kinetic parameters such as apparent Km and Vmax. Two distinct transport activities were identified based on concentration dependence. The first was characterized as high-affinity with a low Km value. The second was identified as low-affinity with a much higher Km value.

Main Results:

The study found that fibroblasts accumulated ascorbic acid up to 20-fold against a concentration gradient. Two distinct transport activities were observed in the cells. The first was a high-affinity transporter with an apparent Km of 6 microM and a Vmax of 203 microM/h. The second was a low-affinity transporter with an apparent Km of 5 mM and a Vmax of 1.8 mM/h. Both transport activities were inhibited by metabolic inhibitors and transport-specific inhibitors. The low-affinity transport could not be explained by simple diffusion. The high-affinity transport activity was comparable to that seen in human neutrophils. However, the low-affinity transporter in fibroblasts differed from that in neutrophils.

Conclusions:

The authors propose that fibroblasts use two distinct transport mechanisms to accumulate ascorbic acid. These findings suggest that two-component transport may be a generalized mechanism in human cells. The high-affinity activity was similar to that observed in neutrophils. However, the low-affinity transporter in fibroblasts was distinct from that in neutrophils. Both transport activities were inhibited by metabolic and transport-specific inhibitors. The study provides the first evidence of this dual transport system in fibroblasts. The results suggest that ascorbic acid transport in human cells may follow a consistent pattern. The authors conclude that fibroblasts may serve as a useful model for studying in situ kinetics of ascorbic acid.

Failed At:

2026-07-10T15:00:48.109394+00:00

The two-component system suggests a generalized mechanism for ascorbic acid accumulation in human cells.

The findings suggest fibroblasts may be a useful model for studying in situ kinetics of ascorbic acid transport.