Calcium sequestering ability of mitochondria modulates influx of calcium through glutamate receptor channel

• Published in: Neurochemical research 2000-12, Vol.25 (12), p.1527-1536
• Main Authors: KANNURPATTI, Sridhar S, JOSHI, Preeti G, JOSHI, Nanda B
• Format: Article
• Language: English
• Subjects: Adenosine Diphosphate - metabolism; Adenosine Triphosphate - metabolism; Animals; Biochemistry and metabolism; Biological and medical sciences; Calcium - metabolism; Carbonyl Cyanide m-Chlorophenyl Hydrazone - pharmacology; Central nervous system; Cerebral Cortex - metabolism; Enzyme Inhibitors - pharmacology; Fundamental and applied biological sciences. Psychology; Glutamic Acid - pharmacology; In Vitro Techniques; Intracellular Membranes - metabolism; Ion Channels - metabolism; Ionophores - pharmacology; Manganese - metabolism; Membrane Potentials - drug effects; Mitochondria - metabolism; Mitochondria - physiology; Oligomycins - pharmacology; Rats; Rats, Sprague-Dawley; Receptors, Glutamate - metabolism; Rotenone - pharmacology; Ruthenium Red - pharmacology; Vertebrates: nervous system and sense organs
• ISSN: 0364-3190; 1573-6903
• DOI: 10.1023/A:1026602100160

The excitotoxicity of glutamate is believed to be mediated by sustained increase in the cytosolic Ca2+ concentration. Mitochondria play a vital role in buffering the cytosolic calcium overload in stimulated neurons. Here we have studied the glutamate induced Ca2+ signals in cortical brain slices under physiological conditions and the conditions that modify the mitochondrial functions. Exposure of slices to glutamate caused a rapid increase in [Ca2+]i followed by a slow and persistently rising phase. The rapid increase in [Ca2+]i was mainly due to influx of Ca2+ through the N-methyl-D-aspartate (NMDA) receptor channels. Glutamate stimulation in the absence of Ca2+ in the extracellular medium elicited a small transient rise in [Ca2+]i which can be attributed to the mobilization of Ca2+ from IP3 sensitive endoplasmic reticulum pools consequent to activation of metabotropic glutamate receptors. The glutamate induced Ca2+ influx was accompanied by depolarization of the mitochondrial membrane, which was inhibited by ruthenium red, the blocker of mitochondrial Ca2+ uniporter. These results imply that mitochondria sequester the Ca2+ loaded into the cytosol by glutamate stimulation. Persistent depolarization of mitochondrial membrane observed in presence of extracellular Ca2+ caused permeability transition and released the sequestered Ca2+ which is manifested as slow rise in [Ca2+]i. Protonophore carbonyl cyanide m-chlorophenyl-hydrazone (CCCP) depolarized the mitochondrial membrane and enhanced the glutamate induced [Ca2+]i response. Contrary to this, treatment of slices with mitochondrial inhibitor oligomycin or ruthenium red markedly reduced the [Ca2+]i response. Combined treatment with oligomycin and rotenone further diminished the [Ca2+]i response and also abolished the CCCP mediated rise in [Ca2+]i. However, rotenone alone had no effect on glutamate induced [Ca2+]i response. These changes in glutamate-induced [Ca2+]i response could not be explained on the basis of deficient mitochondrial Ca2+ sequestration or ATP dependent Ca2+ buffering. The mitochondrial inhibitors reduced the cellular ATP/ADP ratio, however, this would have restrained the ATP dependent Ca2+ buffering processes leading to elevation of [Ca2+]i. In contrast our results showed repression of Ca2+ signal except in case of CCCP which drastically reduced the ATP/ADP ratio. It was inferred that, under the conditions that hamper the Ca2+ sequestering ability of mitochondria, the glutamate induced Ca