Activation of VIP/PACAP type 2 receptor by the peptide histidine isoleucine in astrocytes influences GLAST‐mediated glutamate uptake

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Abstract
Considering the putative neuroprotective role of the vasoactive intestinal peptide (VIP) and the pituitary adenylyl cyclase‐activating polypeptide (PACAP), we investigated the acute modulation of glial glutamate uptake by the structurally related peptide histidine isoleucine (PHI). Using cultures of cortical astrocytes, we demonstrated that a 6 min treatment with 1 μmol/L PHI strongly increased thed‐[3H]‐aspartate uptake velocity from 24.3 ± 1.9 to 46.8 ± 3.5 nmol/mg prot/min. This effect was found to reflect an increase in the activity of the GLAST, the predominant functional glutamate transporter in these cultures. The combination of protein kinase A and C inhibitors was effective in blocking the effect of PHI and the use of peptide antagonists contributed to demonstrate the implication of the VIP/PACAP type 2 receptor (VPAC2). Accordingly, G‐protein activation measures and gene reporter assays revealed the expression of functional PHI‐sensitive receptors in cultured astrocytes. Biotinylation/immunoblotting studies indicated that PHI significantly increased the cell surface expression of the GLAST (by 34.24 ± 8.74 and 43.00 ± 6.36%, when considering the 72 and 55 kDa immunoreactive proteins, respectively). Such cross‐talk between PHI and glutamate transmission systems in glial cells opens attractive perspectives in neuropharmacology.

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