3-NITROPROPIONIC ACID EXACERBATES N-METHYL-D-ASPARTATE TOXICITY IN STRIATAL CULTURE BY MULTIPLE MECHANISMS

We examined the effects of 3-nitropropionic acid-induced succinate deh ydrogenase inhibition on neuronal ATP content, N-methyl-D-aspartate-in duced neuronal death, resting membrane potential, and N-methyl-D-aspar tate-induced changes in cytosolic calcium concentration ([Ca2+](c)) in cultured rat striatal neurons. Exposure of cultures to 3 mM 3-nitropr opionic acid for 3 h did not cause overt toxicity, but reduced ATP con tent by 35%. Treatment with 3-nitropropionic, or removal of Mg2+ from the medium, enhanced subsequent N-methyl-D-asparlate toxicity, reducin g the LC50 from 250 mu M to 12 mu M or 30 mu M, respectively. Even aft er Mg2+ removal, enhancement of N-methyl-D-aspartate toxicity by 3-nit ropropionic acid remained pronounced, with the LC50 further decreasing to 3 mu M. The mean resting membrane potential of neurons treated wit h 3-nitropropionic acid was -37 mV, while that in control neurons was -61 mV. Treatment with 3-nitropropionic did not affect baseline [Ca2+] (c) as determined by fura-2 microfluorimetry. N-methyl-D-aspartate (30 mu M) caused a rapid rise in [Ca2+](c), the initial magnitude of whic h was not affected by 3-nitropropionic acid. However, after a 1-h trea tment, [Ca2+](c) was dramatically higher in 3-nitropropionic acid-trea ted neurons. This increased calcium load was washed out slowly and onl y partially, although calcium in control neurons washed our rapidly an d almost completely. These results suggest that in striatal neurons, t he enhancement of N-methyl-D-aspartate toxicity caused by succinate de hydrogenase inhibition may be due to synergism between partial relief of the Mg2+ blockade of the N-methyl-D-aspartate receptor and other me chanisms, including disruption of neuronal calcium regulation. This sy nergism may be relevant to the neuronal death observed in neurodegener ative disorders. (C) 1998 IBRO. Published by Elsevier Science Ltd.