NMDA receptor activation contributes to a portion of the decreased mitochondrial membrane potential and elevated intracellular free calcium in strain-injured neurons.

In our previous studies, we have shown that in vitro biaxial strain (stretch) injury of neurons in neuronal plus glial cultures increases intracellular free calcium (Ca(2+)) and decreases mitochondrial membrane potential (deltapsi(m)). The goal of this study was to determine whether strain injury, without the addition of exogenous agents, causes glutamate release, and whether NMDA receptor antagonists affect the post-strain injury rise in Ca(2+) and decrease in deltapsi(m). Ca(2+) and deltapsi(m) were measured using the fluorescent indicators fura-2 AM and rhodamine-1,2,3 (rh123). Strain injury of neuronal plus glial cultures caused an immediate 100-200 nM elevation in neuronal [Ca(2+)]i and a decline in neuronal deltapsi(m) by 15 min post-injury. Pretreatment with the NMDA receptor antagonist MK-801 (10 microM) attenuated the Ca(2+) elevation after mild, but not moderate and severe injury. MK-801 pretreatment reduced the decline in deltapsi(m) after mild and moderate, but not after severe injury. The NMDA receptor antagonist D-2-amino-5-phosphonopentanoic acid (APV; 100 microM) had effects similar to MK-801. Simultaneous measurement of Ca(2+) and deltapsi(m) demonstrated a significant correlation and a temporal relationship between Ca(2+) elevation and depression of deltapsi(m). We conclude that NMDA receptor stimulation contributes to some of the changes in Ca(2+) and deltapsi(m) after less severe strain injury. However, after more pronounced injury other mechanisms appear to be more involved.