Ascorbic acid transport and accumulation in human neutrophils.

Area of Science:

• Cellular Biology
• Biochemistry
• Human Physiology

Background:

• Ascorbic acid (vitamin C) is essential for numerous cellular functions.
• Understanding its transport and accumulation in immune cells like neutrophils is critical.
• Previous methods for measuring ascorbic acid in cells were limited.

Purpose of the Study:

• To investigate the transport, accumulation, and distribution of ascorbic acid in human neutrophils.
• To characterize the mechanisms and kinetics of ascorbic acid uptake.
• To quantify intracellular ascorbic acid levels and localization.

Main Methods:

• Utilized a novel assay combining high-performance liquid chromatography (HPLC) and coulometric electrochemical detection.
• Isolated human neutrophils were used for transport and accumulation studies.
• Kinetic analyses (Lineweaver-Burk, Eadie-Hofstee) were performed to determine transporter characteristics.

Main Results:

• Freshly isolated neutrophils contain 1.0-1.4 mM ascorbic acid, primarily in the cytosol (>94%) and not protein-bound.
• Neutrophils accumulate extracellular ascorbic acid via two saturable, temperature-dependent transporters: one high-affinity (Km 2-5 µM) and one low-affinity (Km 6-7 mM).
• These transporters maintain intracellular to extracellular concentration gradients up to 50-fold.

Conclusions:

• Human neutrophils possess efficient, high-affinity and low-affinity transport systems for ascorbic acid.
• The high-affinity transporter is likely saturated under normal physiological conditions in blood.
• The low-affinity transporter operates in its linear phase, contributing to significant ascorbic acid accumulation.