Evidence that intracellular Ca2+ mediates the effect of alpha-ketoisocaproic acid on the phosphorylating system of cytoskeletal proteins from cerebral cortex of immature rats.
In this study we investigated the involvement of Ca2+ on the effects of alpha-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 Ca2+-dependent protein phosphatase, but also by PP2A. We also demonstrated the involvement of Ca2+-dependent mechanisms in the KIC effects using the specific L-voltage-dependent Ca2+ channels (L-VDCC) inhibitor nifedipine, the NMDA antagonist DL-AP5 and the intracellular Ca2+ chelator BAPTA-AM. Blockage of Ca2+ channels or chelating intracellular Ca2+ completely prevented the effects of KIC on the phosphorylating system associated to IF proteins. In addition, we verified that KIC increased 45Ca2+ uptake in brain slices after 3 and 30 min incubation. Taken together, our present data indicate that KIC increase intracellular Ca2+ 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.
Funchal
Cláudia
C
Universidade Federal do Rio Grande do Sul, Instituto de Ciências Básicas da Saúde, Departamento de Bioquímica, Rua Ramiro Barcelos 2600 anexo, 90035-003 Porto Alegre RS, Brazil.
Zamoner
Ariane
A
dos Santos
André Quincozes
AQ
Moretto
Maria Beatriz
MB
Rocha
João B T
JB
Wajner
Moacir
M
Pessoa-Pureur
Regina
R
D000818:Animals; D001345:Autoradiography; D002118:Calcium / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology; D002132:Calcium Radioisotopes; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D003598:Cytoskeletal Proteins / Q000502:physiology*; D004591:Electrophoresis, Polyacrylamide Gel; D015151:Immunoblotting; D007166:Immunosuppressive Agents / Q000494:pharmacology; D066298:In Vitro Techniques; D007651:Keto Acids / Q000494:pharmacology*; D008375:Maple Syrup Urine Disease / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D051381:Rats; D017208:Rats, Wistar; D016559:Tacrolimus / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002132:Calcium Radioisotopes; D003598:Cytoskeletal Proteins; D007166:Immunosuppressive Agents; D007651:Keto Acids; D009419:Nerve Tissue Proteins; C013082:alpha-ketoisocaproic acid; D010749:Phosphoprotein Phosphatases; D002118:Calcium; D016559:Tacrolimus