The role of intracellular Na+ and mitochondria in buffering of kainate-induced intracellular free Ca2+ changes in rat forebrain neurones

We have examined the mechanisms by which cultured central neurones from embryonic rat brain buffer intracellular Ca 2+ loads following kainate receptor activation using fluorescent indicators of [Ca 2+ ] i and [Na + ] i . Stimulation of cultured forebrain neurones with 100 μ m kainate produced a rapid increase in [Ca 2+ ] i that displayed a variable rate of recovery. Kainate also increased [Na + ] i with a response that was slightly slower in onset and markedly slower in recovery. The recovery of [Ca 2+ ] i to baseline was not very sensitive to the [Na + ] i . The magnitude of the increase in [Na + ] i in response to kainate did not correlate well with the [Ca 2+ ] i recovery time, and experimental manipulations that altered [Na + ] i did not have a large impact on the rate of recovery of [Ca 2+ ] i . The recovery of [Ca 2+ ] i to baseline was accelerated by the mitochondrial Na + -Ca 2+ exchange inhibitor CGP-37157, suggesting that the recovery rate is influenced by release of Ca 2+ from a mitochondrial pool and also that variation in the recovery rate is related to the extent of mitochondrial Ca 2+ loading. Kainate did not alter the mitochondrial membrane potential. These studies reveal that mitochondria have a central role in buffering neuronal [Ca 2+ ] i changes mediated by non- N -methyl- d -aspartate (NMDA) glutamate receptors, and that the variation in recovery times following kainate receptor activation reflects a variable degree of mitochondrial Ca 2+ loading. However, unlike NMDA receptor-mediated Ca 2+ loads, kainate receptor activation has minimal effects on mitochondrial function.