Intracellular ascorbic acid inhibits transport of glucose by neurons, but not by astrocytes

Abstract

It has been demonstrated that glutamatergic activity induces ascorbic acid (AA) depletion in astrocytes. Additionally, different data indicate that AA may inhibit glucose accumulation in primary cultures of rat hippocampal neurons. Thus, our hypothesis postulates that AA released from the astrocytes during glutamatergic synaptic activity may inhibit glucose uptake by neurons. We observed that cultured neurons express the sodium-vitamin C cotransporter 2 and the facilitative glucose transporters (GLUT) 1 and 3, however, in hippocampal brain slices GLUT3 was the main transporter detected. Functional activity of GLUTs was confirmed by means of kinetic analysis using 2-deoxy-D-glucose. Therefore, we showed that AA, once accumulated inside the cell, inhibits glucose transport in both cortical and hippocampal neurons in culture. Additionally, we showed that astrocytes are not affected by AA. Using hippocampal slices, we observed that upon blockade of monocarboxylate utilization by a-cyano-4-hydroxycinnamate and after glucose deprivation, glucose could rescue neuronal response to electrical stimulation only if AA uptake is prevented. Finally, using a transwell system of separated neuronal and astrocytic cultures, we observed that glutamate can reduce glucose transport in neurons only in presence of AA-loaded astrocytes, suggesting the essential role of astrocyte-released AA in this effect.

Ascorbic acid participates in a general mechanism for concerted glucose transport inhibition and lactate transport stimulation

“…Cortical neurons were obtained from 17-day-old Wistar rat embryos as described previously [12]. Adult female rats were anesthetized using ether, and embryos were removed.…”

“…Reverse transcription was performed according to Castro and colleagues [12]. For amplification, a cDNA aliquot in a volume of 12.5μl containing 20mM Tris-HCl (pH8.4), 50mM KCl, 1.6mM MgCl 2 , 0.4mM dNTPs, 0.04 units of Taq DNA polymerase (Gibco-BRL, Carlsbad, CA, USA), and 0.4mM primers was incubated at 94°C for 15s, 50°C (PCR for GLUT1 and GLUT3), 55°C (PCR for SVCT2), 60°C (PCR for MCT2) or 62°C (PCR for MCT1) for 30-50s, and 72°C for 30s for 30-50 cycles.…”

“…We have demonstrated that intracellular ascorbic acid is an inhibitor of glucose transport in cortical and hippocampal neurons [12]. Glucose is taken up by neurons through glucose transporters, mainly, GLUT1 and GLUT3 [30,32].…”

Vitamin C and oxidative stress in the seminiferous epithelium

“…SVCT1 and SVCT2 transporters share a 66 % amino acid homology (Boyer et al, 2005), although they are sorted into distinct membrane compartments in epithelial cells. Recently, the expression of SVCT transporters has been described in many cells types and transport results show that ascorbic acid uptake maintains the same kinetic characteristics (Maulén et al, 2003;Castro et al, 2007;.…”

Vitamin C as an antioxidant stabilizes the depressive brain

“…Among other functions, Vitamin C also modulates synaptic activity and neuronal metabolism (Castro et al, 2007(Castro et al, , 2008(Castro et al, , & 2009Harrison and May, 2009). It is concentrated in the brain (Spector and Lorenzo, 1973), the organ responsible for 25% of glucose use of the whole body (Attwell and Laughlin, 2001;Alle et al, 2009).…”