Calcium handling proteins in isolated spinal motoneurons

Amyotrophic lateral sclerosis is characterized by motoneuron degeneration, in which glutamate-induced cell death is thought to play a pathogenic role. This excitotoxic process is mediated by cytosolic Ca 2+ overload. The glutamatergic ionotropic channel molecules, which constitute a major route of Ca 2+ entry, were present on cultured spinal motoneurons. Using ratio RT-PCR, the relative presence in isolated motoneurons of the GluR subunits of the α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptor was evaluated. GluR1 and GluR2 mRNAs were present abundantly, while GluR3 and GluR4 mRNAs were much less abundant. The relative amount of mRNAs encoding the different protein isoforms responsible for Ca 2+ uptake into the internal stores and for controlled release of Ca 2+ from these stores was also determined. For the sarco/endoplasmic reticulum Ca 2+ ATPases (SERCAs), only the SERCA2b class 4 splice variant was found. The inositol 1,4,5-trisphosphate receptor (IP 3 R) mRNAs were mainly transcribed from the IP 3 RI and IP 3 RII genes. Heterogeneity was also observed for the ryanodine receptors (RyR) as the RyR1, RyR2 and RyR3 mRNAs were present.