Objectives: 

The neurotoxin b-N-oxalyl-a,b-diaminopropionic acid (b-ODAP) is a glutamate analogue at a-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)/ kainate (KA) receptors in neurons and therefore potentially acts as an excitotoxic substance. In the present work we aimed at investigating the effect of this toxin on the cellular calcium homeostasis.

Background: 

Chronic exposure to b-ODAP present in L. sativus seeds is proposed as the cause of the neurodegenerative disease neurolathyrism but the mechanism of its action has not been conclusively identified. A key factor in excitotoxic neuronal cell death is a disturbance of the intracellular Ca²⁺ homeostasis, including changes in the capacity of intracellular Ca²⁺ stores like the endoplasmic reticulum (ER) or mitochondria.

Results: 

In this study, the photoprotein aequorin was used in N2a neuroblastoma cells to investigate Ca²⁺ dynamics specifically in the cytosol, ER or mitochondria. Treatment of N2a cells with b-ODAP (24 h) enhanced bradykinin (BK) -induced Ca²⁺ transients and endoplasmic Ca²⁺ uptake. Moreover, mitochondrial Ca²⁺ uptake was stimulated by 35% following stimulation of the cells with bradykinin (BK). Additionally, the mitochondrial membrane potential (Y_m) was shown to become more negative after b-ODAP treatment. Conclusion:

The emerging working hypothesis is that the b-ODAP-triggered hyperpolarisation of Y_m is an early event in the excitotoxicity of this neurotoxin. It causes increased mitochondrial Ca²⁺ uptake, ultimately disturbing the energy metabolism in motor neurons which are cells with an extremely low calcium buffering capacity, eventually leading to cell death. These findings will be further explored in in vitro cultured primary motor neurons.