Brain Mitochondrial Swelling Research Articles

Melatonin Improved Brain Pathologies and Cognitive Dysfunction in Rats with Trastuzumap‐Induced Chemobrain

AbstractBackgroundTrastuzumap (Trz) has been shown to significantly increase the survival rate in human epidermal growth factor receptor (HER2)‐positive breast cancer patients, whereas it also causes neuroinflammation, leading to cognitive impairment, as called “chemobrain”. The exact mechanisms of Trz‐induced chemobrain are not fully understood. Melatonin, a hormone derived from the amino acid tryptophan, has been shown to have the neuroprotection in several pathological conditions. However, the effects of melatonin on brain mitochondrial function, microglial morphology, synaptic plasticity, and cognitive function in Trz‐induced chemobrain have never been investigated.MethodEighteen male Wistar rats were randomly divided into two groups including control group (0.9% NSS, intraperitoneal (i.p.) injection, n=8) and Trz‐treated group (4 mg/kg for 7 days, i.p. injection, n=16). All Trz‐treated rats were randomly divided into two subgroups (n=8/ subgroup) to receive either vehicle (0.9% NSS, daily via oral gavage) or melatonin (10 mg/kg/day, via oral gavage). At the end of experiment protocol, cognitive function was measured, and brains were obtained for further molecular investigation.ResultTrz‐treated rats displayed significantly impaired brain mitochondrial function as indicated by increased ROS production, brain mitochondrial membrane potential change, and brain mitochondrial swelling. These parameters were attenuated in melatonin‐treated Trz‐rats (p<0.05, Figure 1). Consistently, Trz administration decreased microglial complexity, as measured by Sholl analysis, which was ameliorated by melatonin treatment (p<0.05, Figure 1). In addition, the results demonstrated that hippocampal plasticity as indicated by dendritic spine density significantly decreased in Trz‐rats, resulting in cognitive dysfunction as indicated by reducing preferent index of novel object location (NOL) and novel object recognition (NOR) test (p<0.05, Figure 1). Melatonin‐treated Trz‐rats improved hippocampal plasticity by increased dendritic spine density, leading to the improvement of cognition by increased preferent index of NOL and NOR (p<0.05, Figure 1).ConclusionThese findings suggest that melatonin effectively ameliorated cognitive dysfunction in rats with Trz‐induced chemobrain. The novel findings obtained from the present study provided the therapeutic strategies which can be translated into clinical settings for better preventing chemobrain in the future.

Ranolazine Effectively Ameliorated Brain Pathologies and Cognitive Decline in Rats with Trastuzumap‐Induced Chemobrain

AbstractBackgroundChemotherapy can increase survival rate of cancer patients. One of the chemotherapeutic drugs for breast cancer patients is trastuzumap (Trz). Chemotherapy not only helps to kill cancers, but it also causes several adverse effects in the patients, particularly in the brain, known as chemobrain. Chemobrain has been characterized by cognitive decline with brain mitochondrial dysfunction, hippocampal microglial activation, and loss of dendritic spines. Although several types of chemotherapy induce chemobrain, Trz‐induced chemobrain are not clearly elucidated. Ranolazine, a drug that is commonly used to treat the patients with chronic angina, shows benefits on cognitive function in doxorubicin‐induced chemobrain. However, the effects of ranolazine on brain mitochondrial function, hippocampal microglial function, hippocampal dendritic spines, and cognitive function in Trz‐induced chemobrain have never been investigated.MethodsEighteen male Wistar rats were randomly divided into two groups including control group (0.9% NSS, intraperitoneal (i.p.) injection, n=8) and Trz‐treated group (4 mg/kg for 7 days, i.p. injection, n=16). All Trz‐treated rats were randomly divided into two subgroups (n=8/ subgroup) to receive either vehicle (0.9% NSS, daily via oral gavage) or ranolazine (305 mg/kg/day, daily via oral gavage). At the end of experiment protocol, cognitive function was measured, and brains were obtained for further molecular investigation.ResultsThe results demonstrated that vehicle‐treated Trz‐rats significantly increased brain mitochondrial ROS production, increased brain mitochondrial membrane potential change, and increased brain mitochondrial swelling, suggesting brain mitochondrial dysfunction (p<0.05, Figure 1). These parameters were attenuated in ranolazine‐treated Trz‐rats (p<0.05, Figure 1). In addition, the microglial activation was found in vehicle‐treated Trz‐rats as indicated by increased the number of microglial cells, which was suppressed by the ranolazine treatment (p<0.05, Figure 1). Consistently, the dendritic spine density decreased in vehicle‐treated Trz‐rats, leading to cognitive decline (p<0.05, Figure 1). Ranolazine‐treated Trz‐rats showed an increase in dendritic spine density, resulting in the improvement of cognitive function (p<0.05, Figure 1).ConclusionsAll findings suggest that ranolazine effectively ameliorated cognitive decline in rats with Trz‐induced chemobrain. The novel findings obtained from the present study provided the therapeutic strategies which can be translated into clinical settings for better preventing chemobrain in the future.

Effects of high intensity interval training on neuro-cardiovascular dynamic changes and mitochondrial dysfunction induced by high-fat diet in rats.

Background and aimsMitochondrial swelling is involved in the pathogenesis of many human diseases associated with oxidative stress including obesity. One of the strategies for prevention of deleterious effects related to obesity and overweight is engaging in regular physical activity, of which high intensity interval training (HIIT) is efficient in promoting biogenesis and improving the function of mitochondria. Therefore, our aims were to investigate the effects of HIIT on metabolic and neuro-cardiovascular dynamic control and mitochondrial swelling induced by high-fat diet (HFD).Methods and resultsTwenty-three male Wistar rats (60 – 80g) were divided into 4 subgroups: control (C), HIIT, HFD and HFD+HIIT. The whole experimentation period lasted for 22 weeks and HIIT sessions were performed 5 days a week during the last 4 weeks. At the end of the experiments, fasting glucose and insulin tolerance tests were performed. Cerebral microcirculation was analyzed using cortical intravital microscopy for capillary diameter and functional density. Cardiac function and ergoespirometric parameters were also investigated. Mitochondrial swelling was evaluated on brain and heart extracts. HFD promoted an increase on body adiposity (p<0.001), fasting glucose levels (p<0.001), insulin resistance index (p<0.05), cardiac hypertrophy index (p<0.05) and diastolic blood pressure (p<0.05), along with worsened cardiac function (p<0.05), reduced functional cerebral capillary density (p<0.05) and its diameter (p<0.01), and heart and brain mitochondrial function (p<0.001). HFD did not affect any ergoespirometric parameter. After 4 weeks of training, HIIT was able to improve cardiac hypertrophy index, diastolic blood pressure, cerebral functional capillary density (p<0.01) and heart and brain mitochondrial swelling (p<0.001).ConclusionIn animals subjected to HFD, HIIT ameliorated both cerebral mitochondrial swelling and functional capillary density, but it did not improve cardiovascular function suggesting that the cardiovascular dysfunction elicited by HFD was not due to heart mitochondrial swelling.

A novel multi-target ligand (JM-20) protects mitochondrial integrity, inhibits brain excitatory amino acid release and reduces cerebral ischemia injury in vitro and in vivo

We previously showed that JM-20, a novel 1,5-benzodiazepine fused to a dihydropyridine moiety, possessed an anxiolytic profile similar to diazepam and strong neuroprotective activity in different cell models relevant to cerebral ischemia. Here, we investigated whether JM-20 protects against ischemic neuronal damage in vitro and in vivo. The effects of JM-20 were evaluated on hippocampal slices subjected to oxygen and glucose deprivation (OGD). For in vivo studies, Wistar rats were subjected 90 min of middle cerebral artery occlusion (MCAo) and oral administration of JM-20 at 2, 4 and 8 mg/kg 1 h following reperfusion. Twenty-four hours after cerebral blood flow restoration, neurological deficits were scored, and the infarct volume, histopathological changes in cortex, number of hippocampal and striatal neurons, and glutamate/aspartate concentrations in the cerebrospinal fluid were measured. Susceptibility to brain mitochondrial swelling, membrane potential dissipation, H2O2 generation, cytochrome c release, Ca2+ accumulation, and morphological changes in the organelles were assessed 24 h post-ischemia. In vitro, JM-20 (1 and 10 μM) administered during reperfusion significantly reduced cell death in hippocampal slices subjected to OGD. In vivo, JM-20 treatment (4 and 8 mg/kg) significantly decreased neurological deficit scores, edema formation, total infarct volumes and histological alterations in different brain regions. JM-20 treatment also protected brain mitochondria from ischemic damage, most likely by preventing Ca2+ accumulation in organelles. Moreover, an 8-mg/kg JM-20 dose reduced glutamate and aspartate concentrations in cerebrospinal fluid and the deleterious effects of MCAo even when delivered 8 h after blood flow restoration. These results suggest that in rats, JM-20 is a robust neuroprotective agent against ischemia/reperfusion injury with a wide therapeutic window. Our findings support the further examination of potential clinical JM-20 use to treat acute ischemic stroke.

A Tetramethylpyrazine Piperazine Derivate CXC137 Prevents Cell Injury in SH-SY5Y Cells and Improves Memory Dysfunction of Rats with Vascular Dementia

We investigated the effects of CXC137, a tetramethylpyrazine piperazine derivate, on cell damage induced by N-methyl-D-aspartate (NMDA) in human derived neuroblastoma cells (SH-SY5Y) and its effect on memory dysfunction of rats with vascular dementia. It was found that the presence of CXC137 increased SH-SY5Y cells viability by inhibition of cell apoptosis induced by NMDA. These effects of CXC137 were accompanied by increases of the antioxidant superoxide dismutase activity and the level of reduced glutathione, and a decrease of lipid peroxidation product, malondialdehyde. The presence of CXC137 also showed to produce strong inhibition of cellular lactate dehydrogenase leakage, cell apoptosis and intracellular calcium overload. In a vascular dementia rat model established by bilateral common carotid arteries occlusion, treatment with CXC137 from 2 to 35day of post-operation significantly improves the motor performance, spatial learning and memory capability of rats in both the prehensile traction test and Morris water maze test, an effect that was companied by reductions of the animal glutamic acid levels and the degree of brain mitochondrial swelling. These results suggest that CXC137 can improve the memory dysfunction in dementia and thus has important therapeutic potential for the treatment of dementia.

PPARγ Agonist Improves Neuronal Insulin Receptor Function in Hippocampus and Brain Mitochondria Function in Rats with Insulin Resistance Induced by Long Term High-Fat Diets

We previously demonstrated that a high-fat diet (HFD) consumption can cause not only peripheral insulin resistance, but also neuronal insulin resistance. Moreover, the consumption of an HFD has been shown to cause mitochondrial dysfunction in both the skeletal muscle and liver. Rosiglitazone, a peroxizome proliferator-activated receptor-γ ligand, is a drug used to treat type 2 diabetes mellitus. Recent studies suggested that rosiglitazone can improve learning and memory in both human and animal models. However, the effects of rosiglitazone on neuronal insulin resistance and brain mitochondria after the HFD consumption have not yet been investigated. Therefore, we tested the hypothesis that rosiglitazone improves neuronal insulin resistance caused by a HFD via attenuating the dysfunction of neuronal insulin receptors and brain mitochondria. Rosiglitazone (5 mg/kg · d) was given for 14 d to rats that were fed with either a HFD or normal diet for 12 wk. After the 14(th) week, all animals were euthanized, and their brains were removed and examined for insulin-induced long-term depression, neuronal insulin signaling, and brain mitochondrial function. We found that rosiglitazone significantly improved peripheral insulin resistance and insulin-induced long-term depression and increased neuronal Akt/PKB-ser phosphorylation in response to insulin. Furthermore, rosiglitazone prevented brain mitochondrial conformational changes and attenuated brain mitochondrial swelling, brain mitochondrial membrane potential changes, and brain mitochondrial ROS production. Our data suggest that neuronal insulin resistance and the impairment of brain mitochondria caused by a 12-wk HFD consumption can be reversed by rosiglitazone.

Low-molecular-mass peptides from the venom of the Amazonian viper Bothrops atrox protect against brain mitochondrial swelling in rat: Potential for neuroprotection

The neurodegenerative diseases are important causes of morbidity and mortality in Western countries. Common mechanisms of toxicity involving mitochondrial damage have been suggested; however, a definitive treatment has not yet been found. Therefore, there has been great interest in the development of mitochondria-targeted protective compounds for the treatment of neuropathies. Animal toxins represent a promising source of new molecules with neuroprotective activity and potential to originate new drugs. We present here the effects of a low-molecular-mass peptides fraction (Ba-V) from Bothrops atrox snake venom, on rat brain mitochondrial function. Ba-V did not induce the mitochondrial swelling and moreover, was as effective as cyclosporin A (CsA) to inhibit the calcium/phosphate-induced swelling, which indicates its potential to prevent the mitochondrial permeability transition (MPT). The membrane electrochemical potential, the oxygen consumption during states-3 and -4 respirations as well as the respiratory control ratio (RCR) were not affected by Ba-V. Additionally, Ba-V did not induce reactive oxygen species (ROS) generation. Interestingly, Ba-V did not protect against the generation of ROS induced by t-BOH, which suggests a protection mechanism other than ROS scavenging. Given the important role of the mitochondrial damage and, more specifically, of MPT, in the development of neuropathies, Ba-V might be useful in the future strategies for the treatment of these diseases.

Methylmalonate inhibits succinate‐supported oxygen consumption by interfering with mitochondrial succinate uptake

The effect of methylmalonate (MMA) on mitochondrial succinate oxidation has received great attention since it could present an important role in energy metabolism impairment in methylmalonic acidaemia. In the present work, we show that while millimolar concentrations of MMA inhibit succinate-supported oxygen consumption by isolated rat brain or muscle mitochondria, there is no effect when either a pool of NADH-linked substrates or N,N,N',N'-tetramethyl-p-phenylendiamine (TMPD)/ascorbate were used as electron donors. Interestingly, the inhibitory effect of MMA, but not of malonate, on succinate-supported brain mitochondrial oxygen consumption was minimized when nonselective permeabilization of mitochondrial membranes was induced by alamethicin. In addition, only a slight inhibitory effect of MMA was observed on succinate-supported oxygen consumption by inside-out submitochondrial particles. In agreement with these observations, brain mitochondrial swelling experiments indicate that MMA is an important inhibitor of succinate transport by the dicarboxylate carrier. Under our experimental conditions, there was no evidence of malonate production in MMA-treated mitochondria. We conclude that MMA inhibits succinate-supported mitochondrial oxygen consumption by interfering with the uptake of this substrate. Although succinate generated outside the mitochondria is probably not a sig-nificant contributor to mitochondrial energy generation, the physiopathological implications of MMA-induced inhibition of substrate transport by the mitochondrial dicarboxylate carrier are discussed.

Neuroprotective Effects of Propofol in Models of Cerebral Ischemia

Propofol (2,6-diisopropylphenol) has been shown to attenuate neuronal injury in a number of experimental conditions, but studies in models of cerebral ischemia have yielded conflicting results. Moreover, the mechanisms involved in its neuroprotective effects are yet unclear. The authors evaluated the neuroprotective effects of propofol in rat organotypic hippocampal slices exposed to oxygen-glucose deprivation, an in vitro model of cerebral ischemia. To investigate its possible mechanism of action, the authors then examined whether propofol could reduce Ca2+-induced rat brain mitochondrial swelling, an index of mitochondrial membrane permeability, as well as the mitochondrial swelling evoked by oxygen-glucose deprivation in CA1 pyramidal cells by transmission electron microscopy. Finally, they evaluated whether propofol could attenuate the infarct size and improve the neurobehavioral outcome in rats subjected to permanent middle cerebral artery occlusion in vivo. When present in the incubation medium during oxygen-glucose deprivation and the subsequent 24 h recovery period, propofol (10-100 microM) attenuated CA1 injury in hippocampal slices in vitro. Ca2+-induced brain mitochondrial swelling was prevented by 30-100 microM propofol, and so were the ultrastructural mitochondrial changes in CA1 pyramidal cells exposed to oxygen-glucose deprivation. Twenty-four hours after permanent middle cerebral artery occlusion, propofol (100 mg/kg, intraperitoneal) reduced the infarct size by approximately 30% when administered immediately after and up to 30 min after the occlusion. Finally, propofol administered within 30 min after middle cerebral artery occlusion was unable to affect the global neurobehavioral score but significantly preserved spontaneous activity in ischemic rats. These results show that propofol, at clinically relevant concentrations, is neuroprotective in models of cerebral ischemia in vitro and in vivo and that it may act by preventing the increase in neuronal mitochondrial swelling.

Reactive oxygen species induce swelling and cytochrome c release but not transmembrane depolarization in isolated rat brain mitochondria.

1 In this study, we have used isolated brain mitochondria to investigate the effects of superoxide anions (O(2)(-)) on mitochondrial parameters related to apoptosis, such as swelling, potential, enzymatic activity, NAD(P)H, cytochrome c release, and caspase activity. 2 Addition of the reactive oxygen species (ROS) generator KO(2) produced brain mitochondrial swelling, which was blocked by cyclosporin A (CSA), and which was Ca(2+) independent. 3 Calcium induced mitochondrial swelling only at high concentrations and in the presence of succinate. This correlated with the increase in O(2)(-) production detected with hydroethidine in mitochondrial preparations exposed to Ca(2+) and the fact that ROS were required for Ca(2+)-induced mitochondrial swelling. 4 Superoxide anions, but not Ca(2+), decreased citrate synthase and dehydrogenase enzymatic activities and dropped total mitochondrial NAD(P)H levels. 5 Calcium, but not O(2)(-), triggered a rapid loss of mitochondrial potential. Calcium-induced Deltapsi(m) dissipation was inhibited by Ruthenium Red, but not by CSA. 6 Calcium- and superoxide-induced mitochondrial swelling released cytochrome c and increased caspase activity from isolated mitochondria in a CS A-sensitive manner. 7 In summary, superoxide potently triggers mitochondrial swelling and the release of proteins involved in activation of postmitochondrial apoptotic pathways in the absence of mitochondrial depolarization.

Modulation of brain mitochondrial membrane permeability and synaptosomal Ca2+ transport by dopamine oxidation.

Effects of dopamine on the membrane permeability transition, thioredoxin reductase activity, production of free radicals and oxidation of sulfhydryl groups in brain mitochondria and the Ca2+ uptake by Na+-Ca2+ exchange and sulfhydryl oxidation in brain synaptosomes were examined. The brain mitochondrial swelling and the fall of transmembrane potential were altered by pretreatment of dopamine in a dose dependent manner. Depressive effect of dopamine on mitochondrial swelling was reversed by 10 microg/ml catalase, and 10 mM DMSO. The activities of thioredoxin reductase in intact or disrupted mitochondria were decreased by dopamine (1-100 microM), 25 microM Zn2+ and 50 microM Mn2+. Dopamine-inhibited enzyme activity was reversed by 10 microg/ml SOD and 10 microg/ml catalase. Pretreatment of dopamine decreased Ca2+ transport in synaptosomes, which was restored by 10 microg/ml SOD and 10 mM DMSO. Dopamine (1-100 microM) in the medium containing mitochondria produced superoxide anion and hydrogen peroxide, while its effect on nitrite production was very weak. The oxidation of sulfhydryl groups in mitochondria and synaptosomes were enhanced by dopamine with increasing incubation times. Results suggest that dopamine could modulate membrane permeability in mitochondria and calcium transport at nerve terminals, which may be ascribed to the action of free radicals and the loss of reduced sulfhydryl groups.

Brain mitochondrial swelling induced by arachidonic acid and other long chain free fatty acids

Polyunsaturated fatty acids (PUFAs), arachidonic acid in particular, are well known, potent inducers of edema in the brain, while monounsaturated and saturated long chain fatty acids do not possess this quality. This investigation has compared the ability of some free fatty acids (FFAs), known to be released during cerebral ischemia, to induce brain mitochondrial swelling in vitro. The PUFAs tested, especially arachidonic acid (20:4), were more potent in causing swelling than saturated or monounsaturated ones, as measured by the decrease in light absorbance of the mitochondrial suspension. This finding is in line with the unique potency of 20:4 to induce brain edema. Incubation of brain mitochondria with 20:4 for 20 min caused a dose-dependent swelling. ATP-MgCl2 both prevented and reversed this swelling, while binding of the 20:4 by the addition of bovine serum albumin could only prevent but not reverse the swelling. The contraction of the swollen mitochondria appeared to be mediated by a mechanism dependent upon high-energy phosphates, potentiated by MgCl2. The concentration of 20:4 required to induce swelling was about 20 times higher than the concentration required to induce inhibition of mitochondrial respiratory function (L Hillered and P H Chan: J Neurosci Res 19:94-100, 1988a). Moreover, reversal of the swelling occurred without recovery of respiratory function. These results suggest that swelling is a phenomenon of minor importance as an indicator of brain mitochondrial dysfunction, at least when induced by 20:4 in vitro.

Inhibition of brain mitochondrial swelling by idebenone

The effects of idebenone on the swelling of rat brain mitochondria were studied. When FeCl 3 was added to a mitochondrial suspension, a pronounced mitochondrial swelling occured accompanied by the production of lipid peroxide; the two phenomena were closely correlated ( r=0.96, p<0.01). Idebenone inhibited the mitochondrial swelling and lipid peroxidation in a concentration-dependent manner; the concentration giving 50% inhibition was 37 μM for swelling and 53 μM for lipid peroxidation. Metabolites of idebenone also inhibited the lipid peroxidation. These results suggest that idebenone stabilizes the mitochondrial membrane by inhibiting lipid peroxidation in brain mitochondria.

The pharmacological action of pronase-digested egg albumin upon cerebral hypoxia.

The purification of a substance which protects mitochondrial activity against its decay in association with various cerebral pathologies, and the effect of this substance in vitro and in vivo have been mentioned. Defatted egg albumin was hydrolyzed with pronase, and diafiltrated through mesh, to obtain fractions of molecular weight less than 5,000. The diafiltrate was further fractionated using Sephadex G-25 column chromatography, and a fraction which had a protective action against the decay of mitochondrial DNP-ATPase activity was gathered. This digested egg albumin (DEA 5,000 S) showed no immunological reaction and seemingly penetrated well through the cell membrane. DEA 5,000 S prevented the decay of DNP-ATPase activity and swelling of brain mitochondria during aging in vitro. Also, the administration of DEA 5,000 S in vivo shortened the duration of unconsciousness and reduced EEG abnormalities in rats subjected to hypoxia in a special chamber filled with N2 gas. It is suggested that this Digested Egg Albumin has a marked action in restoring the function of metabolically impaired brain.

Metabolism of rat brain mitochondria. Studies on the potassium ion-stimulated oxidation of pyruvate.

1. Rat brain-cortex mitochondria were incubated in media containing 1, 5 or 100mm-K(+) in the presence of ADP, uncoupler (FCCP, carbonyl cyanide p-trifluoro-methoxyphenylhydrazone) or valinomycin while metabolizing pyruvate and malate, or acetylcarnitine and malate or glutamate and malate as substrates. Both the uptake of oxygen and disappearance of substrate were measured under these conditions. 2. With pyruvate and malate as substrate in the presence of both ADP and valinomycin, both the uptake of oxygen and disappearance of pyruvate increased markedly on increasing the K(+) content of the incubation medium from 5 to 100mm-K(+). However, in the presence of uncoupler (FCCP), although the oxygen uptake doubled little change was observed in the rate of disappearance of pyruvate on increasing the K(+) concentration. 3. Only small changes in uptake of substrate and oxygen were observed in the presence of ADP, uncoupler (FCCP) or valinomycin on increasing the K(+) concentration when acetylcarnitine+malate or glutamate+malate were used as substrates by brain mitochondria. 4. Further, increasing the K(+) concentration from 1 to 20mm when rat brain mitochondria were oxidizing a mixture of pyruvate and glutamate in the presence of malate and ADP caused a 30% increase in the respiration rate, 50% increase in the rate of disappearance of pyruvate and an 80% decrease in the rate of disappearance of glutamate. 5. Investigation of the redox state of the cytochromes and the nicotinamide nucleotides in various conditions with either pyruvate or acetylcarnitine as substrates suggested that the specific stimulation of metabolism of pyruvate by K(+) could not be explained by a general stimulation of the electron-transport system. 6. Low-amplitude high-energy swelling of rat brain mitochondria was investigated in both Na(+)- and K(+)-containing media. Swelling of brain mitochondria was much greater in the Na(+)-containing medium and in this medium, the addition of Mg(2+) caused a partial reversal of swelling together with an 85% decrease in the rate of utilization of pyruvate. However, in the K(+)-containing medium, the addition of Mg(2+), although also causing a reversal of swelling, did not affect the rate of disappearance of pyruvate. 7. Measurements of the ATP, NADH/NAD(+) and acetyl-CoA/CoA contents were made under various conditions and no evidence that K(+) concentrations affected these parameters was obtained. 8. The results are discussed in relationship to the physiological significance of the stimulation of pyruvate metabolism by K(+) in rat brain mitochondria. It is proposed that K(+) causes its effects by a direct stimulation of the pyruvate dehydrogenase complex.