High-affinity sodium-vitamin C co-transporters (SVCT) expression in embryonic mouse neurons

The sodium-vitamin C co-transporters SVCT1 and SVCT2 transport the reduced form of vitamin C, ascorbic acid. High expression of the SVCT2 has been dem onstrated in adult neurons and choroid plexus cells by in situ hybridizatio n. Additionally, embryonic mesencephalic dopaminergic neurons express the S VCT2 transporter. However, there have not been molecular and kinetic analys es addressing the expression of SVCTs in cortical embryonic neurons. In thi s work, we confirmed the expression of a SVCT2-like transporter in differen t regions of the fetal mouse brain and in primary cultures of neurons by RT -PCR. Kinetic analysis of the ascorbic acid uptake demonstrated the presenc e of two affinity constants, 103 mum and 8 mum. A K-m of 103 mum correspond s to a similar affinity constant reported for SVCT2, while the Km of 8 pm m ight suggest the expression of a very high affinity transporter for ascorbi c acid. Our uptake analyses also suggest that neurons take up dehydroascorb ic acid, the oxidized form of vitamin C, through the glucose transporters. We consider that the early expression of SVCTs transporters in neurons is i mportant in the uptake of vitamin C, an essential molecule for the fetal br ain physiology. Vitamin C that is found at high concentration in fetal brai n may function in preventing oxidative free radical damage, because antioxi dant radical enzymes mature only late in the developing brain.