Evidence that intracellular Ca 2+ mediates the effect of α-ketoisocaproic acid on the phosphorylating system of cytoskeletal proteins from cerebral cortex of immature rats

Abstract

In this study we investigated the involvement of Ca 2+ on the effects of α-ketoisocaproic acid (KIC), the main metabolite accumulating in maple syrup urine disease (MSUD), on the phosphorylating system associated with the intermediate filament (IF) proteins in slices from cerebral cortex of 9-day-old rats. We first observed that KIC significantly decreased the in vitro phosphorylation of IF proteins in brain slices. KIC-induced dephosphorylation was mediated especially by the protein phosphatase PP2B, a Ca 2+-dependent protein phosphatase, but also by PP2A. We also demonstrated the involvement of Ca 2+-dependent mechanisms in the KIC effects using the specific L-voltage-dependent Ca 2+ channels (L-VDCC) inhibitor nifedipine, the NMDA antagonist DL-AP5 and the intracellular Ca 2+ chelator BAPTA-AM. Blockage of Ca 2+ channels or chelating intracellular Ca 2+ completely prevented the effects of KIC on the phosphorylating system associated to IF proteins. In addition, we verified that KIC increased 45Ca 2+ uptake in brain slices after 3 and 30 min incubation. Taken together, our present data indicate that KIC increase intracellular Ca 2+ levels, probably promoting the activation of calcineurin. These results might be associated with the increased dephosphorylation of the IF proteins in slices of cerebral cortex of immature rats exposed to KIC at similar concentrations from those found in blood and tissues of patients with MSUD.