Phosphorylation of Ca 2+/calmodulin-dependent protein kinase type ii and the α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (ampa) receptor in response to a threonine-devoid diet

Abstract

The anterior piriform cortex (APC) functions as a chemosensor for indispensable amino acid deficiency and responds to this deficiency with increased activity, as indicated by observations including averaged evoked-potentials and c- fos expression in the APC. Little is known of the intracellular signaling mechanisms that mediate this deficiency-related increase in neuronal excitability, but previous studies have shown effects on intracellular Ca 2+ in deficient APC slices in vitro. In the present study we hypothesized that indispensable amino acid deficiency increases intraneuronal Ca 2+, resulting in autophosphorylation of calcium/calmodulin-dependent protein kinase type II (CaMKII) in vivo. Results demonstrated that phosphorylation levels of CaMKII (pCaMKII) in APC neurons increased at 20 and 40 min after a single meal of threonine-devoid diet. Phosphorylation of the α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor subunit (GluR1) at the serine 831 (S831) site was modestly increased in the APC in response to a threonine-devoid meal. The GluR1 subunit also showed increased phosphorylation at the 845 (S845) site, suggesting additional signaling mechanisms. Although phosphorylation of CaMKII was sustained, phosphorylation of the GluR1 subunit returned to control levels by 40 min. These effects of amino acid deficiency did not occur throughout the brain as neither CaMKII nor GluR1 showed increased phosphorylation in the neocortex. These findings support the notion that calcium and glutamate signaling in the APC, but not throughout the brain, are triggered during early responses to amino acid deficiency. They also suggest that longer-term changes in APC neurons in response to such a deficiency may be mediated at least in part by CaMKII.