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

摘要

class="enumerated" style="list-style-type:decimal">We have examined the mechanisms by which cultured central neurones from embryonic rat brain buffer intracellular Ca²⁺ loads following kainate receptor activation using fluorescent indicators of [Ca²⁺]i and [Na⁺]i.Stimulation of cultured forebrain neurones with 100 μm kainate produced a rapid increase in [Ca²⁺]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 [Ca²⁺]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 [Ca²⁺]i recovery time, and experimental manipulations that altered [Na⁺]i did not have a large impact on the rate of recovery of [Ca²⁺]i.The recovery of [Ca²⁺]i to baseline was accelerated by the mitochondrial Na⁺-Ca²⁺ exchange inhibitor CGP-37157, suggesting that the recovery rate is influenced by release of Ca²⁺ from a mitochondrial pool and also that variation in the recovery rate is related to the extent of mitochondrial Ca²⁺ loading. Kainate did not alter the mitochondrial membrane potential.These studies reveal that mitochondria have a central role in buffering neuronal [Ca²⁺]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 Ca²⁺ loading. However, unlike NMDA receptor-mediated Ca²⁺ loads, kainate receptor activation has minimal effects on mitochondrial function.