Keilin's respiratory chain concept and its chemiosmotic consequences

Does acute exposure to thimerosal, an organic mercury compound, affect the mitochondrial function of an infant model?

BACKGROUND

Thimerosal (TM) is a toxic, organometallic mercury compound (which releases ethyl-mercury-containing compounds in aqueous solutions) used as a preservative in vaccines. Mitochondria are organelle which are highly vulnerable to many chemical compounds, including mercury (Hg) and its derivatives.

METHOD

Wistar rats (at 21 days of age) were used to model a child's TM exposure following childhood vaccination, divided in two groups: TM exposed (20 μg/kg/day) and unexposed controls (saline solution), both for 24 h. Atomic Fluorescence Spectrometry was used to quantify the amounts of mercury in tissues. The electron transport chain (ETC) from isolated mitochondria was evaluated using an oxygen electrode. The mitochondrial membrane potential and H2O2 production were analyzed using selective fluorescence probes. The activity of some enzymes (SOD, CAT, GPx, and AChE) and secondary markers of oxidative stress (GSH, GSSG, total free thiol) were also examined in tissues.

RESULTS

Hg accumulation in the brain and liver was higher in exposed animals when compared to the control. Liver-isolated mitochondria showed that TM improved respiratory control by 23%; however, states 3 and 4 of the ETC presented a decrease of 16% and 37%, respectively. Furthermore, brain-isolated mitochondria presented an improvement of 61% in respiratory control. Brain enzyme activities were significantly impacted in TM-exposed rats compared to unexposed rats as follows: decreases in SOD (32%) and AChE (42%) and increases in GPx (79%) and CAT (100%). GPx enzyme activity in the liver was significantly increased (37%). Among secondary oxidative stress markers, the brain's total reduced thiol (SH) concentration was significantly increased (41%).

CONCLUSION

Acute TM treatment exposure in a Wistar rat model mimicking TM exposure in an infant following childhood vaccination significantly damaged brain bioenergetic pathways. This study supports the ability of TM exposure to preferentially damage the nervous system.

Mitochondrial Network: Electric Cable and More

Mitochondria in a cell can unite and organize complex, extended structures that occupy the entire cellular volume, providing an equal supply with energy in the form of ATP synthesized in mitochondria. In accordance with the chemiosmotic concept, the oxidation energy of respiratory substrates is largely stored in the form of an electrical potential difference on the inner membrane of mitochondria. The theory of the functioning of extended mitochondrial structures as intracellular electrical wires suggests that mitochondria provide the fastest delivery of electrical energy through the cellular volume, followed by the use of this energy for the synthesis of ATP, thereby accelerating the process of ATP delivery compared to the rather slow diffusion of ATP in the cell. This analytical review gives the history of the cable theory, lists unsolved critical problems, describes the restructuring of the mitochondrial network and the role of oxidative stress in this process. In addition to the already proven functioning of extended mitochondrial structures as electrical cables, a number of additional functions are proposed, in particular, the hypothesis is put forth that mitochondrial networks maintain the redox potential in the cellular volume, which may vary depending on the physiological state, as a result of changes in the three-dimensional organization of the mitochondrial network (fragmentation/fission-fusion). A number of pathologies accompanied by a violation of the redox status and the participation of mitochondria in them are considered.

The Haves and Have-Nots: The Mitochondrial Permeability Transition Pore across Species

The demonstration that F1FO (F)-ATP synthase and adenine nucleotide translocase (ANT) can form Ca2+-activated, high-conductance channels in the inner membrane of mitochondria from a variety of eukaryotes led to renewed interest in the permeability transition (PT), a permeability increase mediated by the PT pore (PTP). The PT is a Ca2+-dependent permeability increase in the inner mitochondrial membrane whose function and underlying molecular mechanisms have challenged scientists for the last 70 years. Although most of our knowledge about the PTP comes from studies in mammals, recent data obtained in other species highlighted substantial differences that could be perhaps attributed to specific features of F-ATP synthase and/or ANT. Strikingly, the anoxia and salt-tolerant brine shrimp Artemia franciscana does not undergo a PT in spite of its ability to take up and store Ca2+ in mitochondria, and the anoxia-resistant Drosophila melanogaster displays a low-conductance, selective Ca2+-induced Ca2+ release channel rather than a PTP. In mammals, the PT provides a mechanism for the release of cytochrome c and other proapoptotic proteins and mediates various forms of cell death. In this review, we cover the features of the PT (or lack thereof) in mammals, yeast, Drosophila melanogaster, Artemia franciscana and Caenorhabditis elegans, and we discuss the presence of the intrinsic pathway of apoptosis and of other forms of cell death. We hope that this exercise may help elucidate the function(s) of the PT and its possible role in evolution and inspire further tests to define its molecular nature.

Questioning rotary functionality in the bacterial flagellar system and proposing a murburn model for motility

Bacterial flagellar system (BFS) was the primary example of a purported 'rotary-motor' functionality in a natural assembly. This mandates the translation of a circular motion of components inside into a linear displacement of the cell body outside, which is supposedly orchestrated with the following features of the BFS: (i) A chemical/electrical differential generates proton motive force (pmf, including a trans-membrane potential, TMP), which is electro-mechanically transduced by inward movement of protons via BFS. (ii) Membrane-bound proteins of BFS serve as stators and the slender filament acts as an external propeller, culminating into a hook-rod that pierces the membrane to connect to a 'broader assembly of deterministically movable rotor'. We had disclaimed the purported pmf/TMP-based respiratory/photosynthetic physiology involving Complex V, which was also perceived as a 'rotary machine' earlier. We pointed out that the murburn redox logic was operative therein. We pursue the following similar perspectives in BFS-context: (i) Low probability for the evolutionary attainment of an ordered/synchronized teaming of about two dozen types of proteins (assembled across five-seven distinct phases) towards the singular agendum of rotary motility. (ii) Vital redox activity (not the gambit of pmf/TMP!) powers the molecular and macroscopic activities of cells, including flagella. (iii) Flagellar movement is noted even in ambiances lacking/countering the directionality mandates sought by pmf/TMP. (iv) Structural features of BFS lack component(s) capable of harnessing/achieving pmf/TMP and functional rotation. A viable murburn model for conversion of molecular/biochemical activity into macroscopic/mechanical outcomes is proposed herein for understanding BFS-assisted motility. HIGHLIGHTSThe motor-like functionalism of bacterial flagellar system (BFS) is analyzedProton/Ion-differential based powering of BFS is unviable in bacteriaUncouplers-sponsored effects were misinterpreted, resulting in a detour in BFS researchThese findings mandate new explanation for nano-bio-mechanical movements in BFSA minimalist murburn model for the bacterial flagella-aided movement is proposedCommunicated by Ramaswamy H. Sarma.

Inflammation, Mitochondria and Natural Compounds Together in the Circle of Trust

Human diseases are characterized by the perpetuation of an inflammatory condition in which the levels of Reactive Oxygen Species (ROS) are quite high. Excessive ROS production leads to DNA damage, protein carbonylation and lipid peroxidation, conditions that lead to a worsening of inflammatory disorders. In particular, compromised mitochondria sustain a stressful condition in the cell, such that mitochondrial dysfunctions become pathogenic, causing human disorders related to inflammatory reactions. Indeed, the triggered inflammation loses its beneficial properties and turns harmful if dysregulation and dysfunctions are not addressed. Thus, reducing oxidative stress with ROS scavenger compounds has proven to be a successful approach to reducing inflammation. Among these, natural compounds, in particular, polyphenols, alkaloids and coenzyme Q₁₀, thanks to their antioxidant properties, are capable of inhibiting the activation of NF-κB and the expression of target genes, including those involved in inflammation. Even more, clinical trials, and in vivo and in vitro studies have demonstrated the antioxidant and anti-inflammatory effects of phytosomes, which are capable of increasing the bioavailability and effectiveness of natural compounds, and have long been considered an effective non-pharmacological therapy. Therefore, in this review, we wanted to highlight the relationship between inflammation, altered mitochondrial oxidative activity in pathological conditions, and the beneficial effects of phytosomes. To this end, a PubMed literature search was conducted with a focus on various in vitro and in vivo studies and clinical trials from 2014 to 2022.

The evolution of the human mitochondrial bc1 complex- adaptation for reduced rate of superoxide production?

The mitochondrial bc1 complex is a major source of mitochondrial superoxide. While bc1-generated superoxide plays a beneficial signaling role, excess production of superoxide lead to aging and degenerative diseases. The catalytic core of bc1 comprises three peptides -cytochrome b, Fe-S protein, and cytochrome c1. All three core peptides exhibit accelerated evolution in anthropoid primates. It has been suggested that the evolution of cytochrome b in anthropoids was driven by a pressure to reduce the production of superoxide. In humans, the bc1 core peptides exhibit anthropoid-specific substitutions that are clustered near functionally critical sites that may affect the production of superoxide. Here we compare the high-resolution structures of bovine, mouse, sheep and human bc1 to identify structural changes that are associated with human-specific substitutions. Several cytochrome b substitutions in humans alter its interactions with other subunits. Most significantly, there is a cluster of seven substitutions, in cytochrome b, the Fe-S protein, and cytochrome c1 that affect the interactions between these proteins at the tether arm of the Fe-S protein and may alter the rate of ubiquinone oxidation and the rate of superoxide production. Another cluster of substitutions near heme bH and the ubiquinone reduction site, Qi, may affect the rate of ubiquinone reduction and thus alter the rate of superoxide production. These results are compatible with the hypothesis that cytochrome b in humans (and other anthropoid primates) evolve to reduce the rate of production of superoxide thus enabling the exceptional longevity and exceptional cognitive ability of humans.

Kinetic Mathematical Modeling of Oxidative Phosphorylation in Cardiomyocyte Mitochondria

Oxidative phosphorylation (OXPHOS) is an oxygen-dependent process that consumes catabolized nutrients to produce adenosine triphosphate (ATP) to drive energy-dependent biological processes such as excitation-contraction coupling in cardiomyocytes. In addition to in vivo and in vitro experiments, in silico models are valuable for investigating the underlying mechanisms of OXPHOS and predicting its consequences in both physiological and pathological conditions. Here, we compare several prominent kinetic models of OXPHOS in cardiomyocytes. We examine how their mathematical expressions were derived, how their parameters were obtained, the conditions of their experimental counterparts, and the predictions they generated. We aim to explore the general landscape of energy production mechanisms in cardiomyocytes for future in silico models.

Sphingosine as a New Antifungal Agent against Candida and Aspergillus spp

This study investigated whether sphingosine is effective as prophylaxis against Aspergillus spp. and Candida spp. In vitro experiments showed that sphingosine is very efficacious against A. fumigatus and Nakeomyces glabrataa (formerly named C. glabrata). A mouse model of invasive aspergillosis showed that sphingosine exerts a prophylactic effect and that sphingosine-treated animals exhibit a strong survival advantage after infection. Furthermore, mechanistic studies showed that treatment with sphingosine leads to the early depolarization of the mitochondrial membrane potential (Δψm) and the generation of mitochondrial reactive oxygen species and to a release of cytochrome C within minutes, thereby presumably initiating apoptosis. Because of its very good tolerability and ease of application, inhaled sphingosine should be further developed as a possible prophylactic agent against pulmonary aspergillosis among severely immunocompromised patients.

The mitochondrial chaperone TRAP1 regulates F-ATP synthase channel formation

Binding of the mitochondrial chaperone TRAP1 to client proteins shapes bioenergetic and proteostatic adaptations of cells, but the panel of TRAP1 clients is only partially defined. Here we show that TRAP1 interacts with F-ATP synthase, the protein complex that provides most cellular ATP. TRAP1 competes with the peptidyl-prolyl cis-trans isomerase cyclophilin D (CyPD) for binding to the oligomycin sensitivity-conferring protein (OSCP) subunit of F-ATP synthase, increasing its catalytic activity and counteracting the inhibitory effect of CyPD. Electrophysiological measurements indicate that TRAP1 directly inhibits a channel activity of purified F-ATP synthase endowed with the features of the permeability transition pore (PTP) and that it reverses PTP induction by CyPD, antagonizing PTP-dependent mitochondrial depolarization and cell death. Conversely, CyPD outcompetes the TRAP1 inhibitory effect on the channel. Our data identify TRAP1 as an F-ATP synthase regulator that can influence cell bioenergetics and survival and can be targeted in pathological conditions where these processes are dysregulated, such as cancer.

The mitochondrial permeability transition: Recent progress and open questions

Major progress has been made in defining the basis of the mitochondrial permeability transition, a Ca²⁺ -dependent permeability increase of the inner membrane that has puzzled mitochondrial research for almost 70 years. Initially considered an artefact of limited biological interest by most, over the years the permeability transition has raised to the status of regulator of mitochondrial ion homeostasis and of druggable effector mechanism of cell death. The permeability transition is mediated by opening of channel(s) modulated by matrix cyclophilin D, the permeability transition pore(s) (PTP). The field has received new impulse (a) from the hypothesis that the PTP may originate from a Ca²⁺ -dependent conformational change of F-ATP synthase and (b) from the reevaluation of the long-standing hypothesis that it originates from the adenine nucleotide translocator (ANT). Here, we provide a synthetic account of the structure of ANT and F-ATP synthase to discuss potential and controversial mechanisms through which they may form high-conductance channels; and review some intriguing findings from the wealth of early studies of PTP modulation that still await an explanation. We hope that this review will stimulate new experiments addressing the many outstanding problems, and thus contribute to the eventual solution of the puzzle of the permeability transition.

The gene order in the nuo-operon is not essential for the assembly of E. coli complex I

Energy-converting NADH: ubiquinone oxidoreductase, respiratory complex I, plays an important role in cellular energy metabolism. Bacterial complex I is generally composed of 14 different subunits, seven of which are membranous and the other seven are globular proteins. They are encoded by the nuo-operon, whose gene order is strictly conserved in bacteria. The operon starts with nuoA encoding a membranous subunit followed by genes encoding globular subunits. To test the idea that NuoA acts as a seed to initiate the assembly of the complex in the membrane, we generated mutants that either lacked nuoA or contain nuoA at a different position within the operon. To enable the detection of putative assembly intermediates, the globular subunit NuoF and the membranous subunit NuoM were individually decorated with the fluorescent protein mCherry. Deletion of nuoA led to the assembly of an inactive complex in the membrane containing NuoF and NuoM. Re-arrangement of nuoA within the nuo-operon led to a slightly diminished amount of complex I in the membrane that was fully active. Thus, nuoA but not its distinct position in the operon is required for the assembly of E. coli complex I. Furthermore, we detected a previously unknown assembly intermediate in the membrane containing NuoM that is present in greater amounts than complex I.

Study of Ren, RexA, and RexB Functions Provides Insight Into the Complex Interaction Between Bacteriophage λ and Its Host, Escherichia coli

The phage λ rexA and rexB genes are expressed from the P RM promoter in λ lysogens along with the cI repressor gene. RexB is also expressed from a second promoter, P LIT, embedded in rexA. The combined expression of rexA and rexB causes Escherichia coli to be more ultraviolet (UV) sensitive. Sensitivity is further increased when RexB levels are reduced by a defect in the P LIT promoter, thus the degree of sensitivity can be modulated by the ratio of RexA/RexB. Expression of the phage λ ren gene rescues this host UV sensitive phenotype; Ren also rescues an aberrant lysis phenotype caused by RexA and RexB. We screened an E. coli two-hybrid library to identify bacterial proteins with which each of these phage proteins physically interact. The results extend previous observations concerning λ Rex exclusion and show the importance of E. coli electron transport and sulfur assimilation pathways for the phage.

Molecular Biology of Microbial Rhodopsins

Research on type 1 rhodopsins spans now a history of 50 years. Originally, just archaeal ion pumps and sensors have been discovered. However, with modern genetic techniques and gene sequencing tools, more and more proteins were identified in all kingdoms of life. Spectroscopic and other biophysical studies revealed quite diverse functions. Ion pumps, sensors, and channels are imprinted in the same seven-helix transmembrane protein scaffold carrying a retinal prosthetic group. In this review, molecular biology methods are described, which enabled the elucidation of their function and structure leading to optogenetic applications.

Metabolic Therapy of Heart Failure: Is There a Future for B Vitamins?

Heart failure (HF) is a plague of the aging population in industrialized countries that continues to cause many deaths despite intensive research into more effective treatments. Although the therapeutic arsenal to face heart failure has been expanding, the relatively short life expectancy of HF patients is pushing towards novel therapeutic strategies. Heart failure is associated with drastic metabolic disorders, including severe myocardial mitochondrial dysfunction and systemic nutrient deprivation secondary to severe cardiac dysfunction. To date, no effective therapy has been developed to restore the cardiac energy metabolism of the failing myocardium, mainly due to the metabolic complexity and intertwining of the involved processes. Recent years have witnessed a growing scientific interest in natural molecules that play a pivotal role in energy metabolism with promising therapeutic effects against heart failure. Among these molecules, B vitamins are a class of water soluble vitamins that are directly involved in energy metabolism and are of particular interest since they are intimately linked to energy metabolism and HF patients are often B vitamin deficient. This review aims at assessing the value of B vitamin supplementation in the treatment of heart failure.

Effect of extracellular volume on the energy stored in transmembrane concentration gradients

The amount of energy that can be retrieved from a concentration gradient across a membrane separating two compartments depends on the relative size of the compartments. Having a larger low-concentration compartment is in general beneficial. It is shown here analytically that the retrieved energy further increases when the high-concentration compartment shrinks during the mixing process, and a general formula is derived for the energy when the ratio of transported solvent to solute varies. These calculations are then applied to the interstitial compartment of the brain, which is rich in Na^{+} and Cl^{-} ions and poor in K^{+}. The reported shrinkage of this compartment, and swelling of the neurons, during oxygen deprivation is shown to enhance the energy recovered from NaCl entering the neurons. The slight loss of energy on the part of K^{+} can be compensated for by the uptake of K^{+} ions by glial cells. In conclusion, the present study proposes that the reported fluctuations in the size of the interstitial compartment of the brain (expansion during sleep and contraction during oxygen deprivation) optimize the amount of energy that neurons can store in, and retrieve from, their ionic concentration gradients.

Extended supercomplex contains type-II NADH dehydrogenase, cytochrome bcc complex, and aa3 oxidase in the respiratory chain of Corynebacterium glutamicum

To clarify the precise subunit composition of the respiratory supercomplex of Corynebacterium glutamicum, several wash conditions were examined. MEGA (9 + 10) wash-buffer (0.5%) was used for this purpose and two-step column chromatography was performed. Almost equal amounts of cytochrome c, b, and a were observed in the purified fraction, estimated by their different absorption spectra. The 833 kDa and 685 kDa bands were observed in the clear native polyacrylamide gel electrophoresis (CN-PAGE) of the purified fraction. Both bands were stained using N,N',N',N-tetramethyl-p-phenylenediamine (TMPD) oxidase dye, and the 833 kDa band was also stained using NADH oxidase dye. The 3D map reconstructed from the 833 kDa band indicated that the bcc complex and aa₃ oxidase are heterodimers. Lastly, electron transfer from NADH to the bcc-aa₃ supercomplex was observed. The 833 kDa band is the supercomplex, which includes the heterodimer cytochrome bcc complex and cytochrome aa₃ oxidase, as well as the monomer NDH-II. Hence, we termed the 833 kDa band the extended supercomplex (ESC).

Experimental Approaches for Testing the Hypothesis of the Emergence of Life at Submarine Alkaline Vents

Since the pioneering experimental work performed by Urey and Miller around 70 years ago, several experimental works have been developed for approaching the question of the origin of life based on very few well-constructed hypotheses. In recent years, attention has been drawn to the so-called alkaline hydrothermal vents model (AHV model) for the emergence of life. Since the first works, perspectives from complexity sciences, bioenergetics and thermodynamics have been incorporated into the model. Consequently, a high number of experimental works from the model using several tools have been developed. In this review, we present the key concepts that provide a background for the AHV model and then analyze the experimental approaches that were motivated by it. Experimental tools based on hydrothermal reactors, microfluidics and chemical gardens were used for simulating the environments of early AHVs on the Hadean Earth (~4.0 Ga). In addition, it is noteworthy that several works used techniques from electrochemistry to investigate phenomena in the vent-ocean interface for early AHVs. Their results provided important parameters and details that are used for the evaluation of the plausibility of the AHV model, and for the enhancement of it.

In Silico Modeling of the Mitochondrial Pumping Complexes with Markov State Models

The mechanism of proton pumping by the mitochondrial electron transport chain complexes is still enigmatic after decades of research. Recently, there has been interest in in silico Markov state models to model the mitochondrial pumping complexes at the microscopic level, and this chapter describes the methods of constructing and simulating such models.

Mitochondrial transplantation in cardiomyocytes: foundation, methods, and outcomes

Mitochondrial transplantation is emerging as a novel cellular biotherapy to alleviate mitochondrial damage and dysfunction. Mitochondria play a crucial role in establishing cellular homeostasis and providing cell with the energy necessary to accomplish its function. Owing to its endosymbiotic origin, mitochondria share many features with their bacterial ancestors. Unlike the nuclear DNA, which is packaged into nucleosomes and protected from adverse environmental effects, mitochondrial DNA are more prone to harsh environmental effects, in particular that of the reactive oxygen species. Mitochondrial damage and dysfunction are implicated in many diseases ranging from metabolic diseases to cardiovascular and neurodegenerative diseases, among others. While it was once thought that transplantation of mitochondria would not be possible due to their semiautonomous nature and reliance on the nucleus, recent advances have shown that it is possible to transplant viable functional intact mitochondria from autologous, allogenic, and xenogeneic sources into different cell types. Moreover, current research suggests that the transplantation could positively modulate bioenergetics and improve disease outcome. Mitochondrial transplantation techniques and consequences of transplantation in cardiomyocytes are the theme of this review. We outline the different mitochondrial isolation and transfer techniques. Finally, we detail the consequences of mitochondrial transplantation in the cardiovascular system, more specifically in the context of cardiomyopathies and ischemia.

Mitochondria and the permeability transition pore in cancer metabolic reprogramming

Mitochondria are a major source of ATP provision as well as cellular suicidal weapon store. Accumulating evidences demonstrate that mitochondrial bioenergetics, biosynthesis and signaling are important mediators of tumorigenesis. Metabolic plasticity enables cancer cell reprogramming to cope with cellular and environmental alterations, a process requires mitochondria biology. Mitochondrial metabolism emerges to be a promising arena for cancer therapeutic targets. The permeability transition pore (PTP) participates in physiological Ca²⁺ and ROS homeostasis as well as cell death depending on the open state. The hypothesis that PTP forms from F-ATP synthase provides clues to the potential collaborative role of mitochondrial respiration and PTP in regulating cancer cell fate and metabolic reprogramming.

Sulfide affects the mitochondrial respiration, the Ca2+-activated F1FO-ATPase activity and the permeability transition pore but does not change the Mg2+-activated F1FO-ATPase activity in swine heart mitochondria

In mammalian cells enzymatic and non-enzymatic pathways produce H₂S, a gaseous transmitter which recently emerged as promising therapeutic agent and modulator of mitochondrial bioenergetics. To explore this topic, the H₂S donor NaHS, at micromolar concentrations, was tested on swine heart mitochondria. NaHS did not affect the F₁F_O-ATPase activated by the natural cofactor Mg², but, when Mg²⁺ was replaced by Ca²⁺, a slight 15% enzyme inhibition at 100 µM NaHS was shown. Conversely, both the NADH-O₂ and succinate-O₂ oxidoreductase activities were totally inhibited by 200 μM NaHS with IC₅₀ values of 61.6 ± 4.1 and 16.5 ± 4.6 μM NaHS, respectively. Since the mitochondrial respiration was equally inhibited by NaHS at both first or second respiratory substrates sites, the H₂S generation may prevent the electron transfer from complexes I and II to downhill respiratory chain complexes, probably because H₂S competes with O₂ in complex IV, thus reducing membrane potential as a consequence of the cytochrome c oxidase activity inhibition. The Complex IV blockage by H₂S was consistent with the linear concentration-dependent NADH-O₂ oxidoreductase inhibition and exponential succinate-O₂ oxidoreductase inhibition by NaHS, whereas the coupling between substrate oxidation and phosphorylation was unaffected by NaHS. Even if H₂S is known to cause sulfhydration of cysteine residues, thiol oxidizing (GSSG) or reducing (DTE) agents, did not affect the F₁F_O-ATPase activities and mitochondrial respiration, thus ruling out any involvement of post-translational modifications of thiols. The permeability transition pore, the lethal channel which forms when the F₁F_O-ATPase is stimulated by Ca²⁺, did not open in the presence of NaHS, which showed a similar effect to ruthenium red, thus suggesting a putative Ca²⁺ transport cycle inhibition.

Co-purification of nitrate reductase 1 with components of the cytochrome bcc-aa3 oxidase supercomplex from spores of Streptomyces coelicolor A3(2)

In order to reduce nitrate in vivo, the spore‐specific respiratory nitrate reductase, Nar1, of Streptomyces coelicolor relies on an active cytochrome bcc‐aa₃ oxidase supercomplex (bcc‐aa₃ supercomplex). This suggests that membrane‐associated Nar1, comprising NarG1, NarH1, and NarI1 subunits, might not act as a classical menaquinol oxidase but could either receive electrons from the bcc‐aa₃ supercomplex, or require the supercomplex to stabilize the reductase in the membrane to allow it to function. To address the biochemical basis for this dependence on the bcc‐aa₃ supercomplex, we purified two different Strep‐tagged variants of Nar1 and enriched the native enzyme complex from spore extracts using different chromatographic and electrophoretic procedures. Polypeptides associated with the isolated Nar1 complexes were identified using mass spectrometry and included components of the bcc‐aa₃ supercomplex, along with an alternative, spore‐specific cytochrome b component, QcrB3. Surprisingly, we also co‐enriched the Nar3 enzyme with Nar1 from the wild‐type strain of S. coelicolor. Two differentially migrating active Nar1 complexes could be identified after clear native polyacrylamide gel electrophoresis; these had masses of approximately 450 and 250 kDa. The distribution of active Nar1 in these complexes was influenced by the presence of cytochrome bd oxidase and by QcrB3; the presence of the latter shifted Nar1 into the larger complex. Together, these data suggest that several respiratory complexes can associate in the spore membrane, including Nar1, Nar3, and the bcc‐aa₃ supercomplex. Moreover, these findings provide initial support for the hypothesis that Nar1 and the bcc‐aa₃ supercomplex physically associate.

Protonic conductor: better understanding neural resting and action potential

With the employment of the transmembrane electrostatic proton localization theory with a new membrane potential equation, neural resting and action potential is now much better understood as the voltage contributed by the localized protons/cations at a neural liquid- membrane interface. Accordingly, the neural resting/action potential is essentially a protonic/cationic membrane capacitor behavior. It is now understood with a newly formulated action potential equation: when action potential is <0 (negative number), the localized protons/cations charge density at the liquid-membrane interface along the periplasmic side is >0 (positive number); when the action potential is >0, the concentration of the localized protons and localized nonproton cations is <0, indicating a "depolarization" state. The nonlinear curve of the localized protons/cations charge density in the real-time domain of an action potential spike appears as an inverse mirror image to the action potential. The newly formulated action potential equation provides biophysical insights for neuron electrophysiology, which may represent a complementary development to the classic Goldman-Hodgkin-Katz equation. With the use of the action potential equation, the biological significance of axon myelination is now also elucidated as to provide protonic insulation and prevent any ions both inside and outside of the neuron from interfering with the action potential signal, so that the action potential can quickly propagate along the axon with minimal (e.g., 40 times less) energy requirement.NEW & NOTEWORTHY The newly formulated action potential equation provides biophysical insights for neuron electrophysiology, which may represent a complementary development to the classic Goldman-Hodgkin-Katz equation. The nonlinear curve of the localized protons/cations charge density in the real-time domain of an action potential spike appears as an inverse mirror image to the action potential. The biological significance of axon myelination is now elucidated as to provide protonic insulation and prevent any ions from interfering with action potential signal.

What is the Role of Lipid Membrane-embedded Quinones in Mitochondria and Chloroplasts? Chemiosmotic Q-cycle versus Murburn Reaction Perspective

Quinones are found in the lipid membranes of prokaryotes like E. coli and cyanobacteria, and are also abundant in eukaryotic mitochondria and chloroplasts. They are intricately involved in the reaction mechanism of redox phosphorylations. In the Mitchellian chemiosmotic school of thought, membrane-lodged quinones are perceived as highly mobile conveyors of two-electron equivalents from the first leg of Electron Transport Chain (ETC) to the 'second pit-stop' of Cytochrome bc₁ or b₆f complex (CBC), where they undergo a regenerative 'Q-cycle'. In Manoj's murburn mechanism, the membrane-lodged quinones are perceived as relatively slow-moving one- or two- electron donors/acceptors, enabling charge separation and the CBC resets a one-electron paradigm via 'turbo logic'. Herein, we compare various purviews of the two mechanistic schools with respect to: constraints in mobility, protons' availability, binding of quinones with proteins, structural features of the protein complexes, energetics of reaction, overall reaction logic, etc. From various perspectives, the murburn mechanism appeals as a viable alternative explanation well-rooted in thermodynamics/kinetics and one which lends adequate structure-function correlations for the roles of quinones, lipid membrane and associated proteins.

The fluid-mosaic membrane theory in the context of photosynthetic membranes: Is the thylakoid membrane more like a mixed crystal or like a fluid?

Since the publication of the fluid-mosaic membrane theory by Singer and Nicolson in 1972 generations of scientists have adopted this fascinating concept for all biological membranes. Assuming the membrane as a fluid implies that the components embedded in the lipid bilayer can freely diffuse like swimmers in a water body. During the detailed biochemical analysis of the thylakoid protein components of chloroplasts from higher plants and algae, in the '80 s and '90 s it became clear that photosynthetic membranes are not homogeneous either in the vertical or the lateral directions. The lateral heterogeneity became obvious by the differentiation of grana and stroma thylakoids, but also the margins have been identified with a highly specific protein pattern. Further refinement of the fluid mosaic model was needed to take into account the presence of non-bilayer lipids, which are the most abundant lipids in all energy-converting membranes, and the polymorphism of lipid phases, which has also been documented in thylakoid membranes. These observations lead to the question, how mobile the components are in the lipid phase and how this ordering is made and maintained and how these features might be correlated with the non-bilayer propensity of the membrane lipids. Assuming instead of free diffusion, a "controlled neighborhood" replaced the model of fluidity by the model of a "mixed crystal structure". In this review we describe why basic photosynthetic regulation mechanisms depend on arrays of crystal-like lipid-protein macro-assemblies. The mechanisms which define the ordering in macrodomains are still not completely clear, but some recent experiments give an idea how this fascinating order is produced, adopted and maintained. We use the operation of the xanthophyll cycle as a rather well understood model challenging and complementing the standard Singer-Nicolson model via assigning special roles to non-bilayer lipids and non-lamellar lipid phases in the structure and function of thylakoid membranes.

Human adaptation to hypoxia in critical illness

The syndrome of critical illness is a complex physiological stressor that can be triggered by diverse pathologies. It is widely believed that organ dysfunction and death result from bioenergetic failure caused by inadequate cellular oxygen supply. Teleologically, life has evolved to survive in the face of stressors by undergoing a suite of adaptive changes. Adaptation not only comprises alterations in systemic physiology but also involves molecular reprogramming within cells. The concept of cellular adaptation in critically ill patients is a matter of contention in part because medical interventions mask underlying physiology, creating the artificial construct of "chronic critical illness," without which death would be imminent. Thus far, the intensive care armamentarium has not targeted cellular metabolism to preserve a temporary equilibrium but instead attempts to normalize global oxygen and substrate delivery. Here, we review adaptations to hypoxia that have been demonstrated in cellular models and in human conditions associated with hypoxia, including the hypobaric hypoxia of high altitude, the intrauterine low-oxygen environment, and adult myocardial hibernation. Common features include upregulation of glycolytic ATP production, enhancement of respiratory efficiency, downregulation of mitochondrial density, and suppression of energy-consuming processes. We argue that these innate cellular adaptations to hypoxia represent potential avenues for intervention that have thus far remained untapped by intensive care medicine.

Gene disruption of ribosomal protein L5 (RPL5) decreased the sensitivity of CHO-K1 cells to uncoupler carbonylcyanide-3-chlorophenylhydrazone

Protonophoric uncoupler carbonylcyanide-3-chlorophenylhydrazone (CCCP) decreases the proton motive force (ΔP) of the mitochondrial inner membrane and results in inhibition of oxidative phosphorylation. In this study, a CCCP-resistant clone was isolated from a random gene trap insertional mutant library of Chinese hamster ovary (CHO)-K1 cells which was constructed by infecting a retrovirus vector, ROSAβgeo. Although we expected the isolation of the mutants defective in nuclear genes responsible for mitochondrial functions, the disrupted gene of the isolated mutant that we named R1 cells was identified as one of the alleles for ribosomal protein 5 of large subunit (RPL5). The R1 cells express as much as 80% RPL5 protein compared with the parental CHO-K1 cells, possibly due to enhanced transcription from a remaining wild-type RPL5 allele in R1 cells. Furthermore, the protein amount is not decreased by CCCP in R1 cells, in contrast to its clear reduction by CCCP in parental cells. Since mutations of RPL5 and other ribosomal proteins are responsible for the ribosomopathies and cancer, the present mutant may be a useful cellular model of such human diseases from a viewpoint of energy metabolism as well as a tool for the study of ribosome biogenesis and extra-ribosomal function of the RPL5 protein.

Anaerobic nitrate respiration in the aerobe Streptomyces coelicolor A3(2): helping maintain a proton gradient during dormancy

Respiratory nitrate reductases (Nar) catalyse the reduction of nitrate to nitrite, coupling this process to energy conservation. The obligate aerobic actinobacterium Streptomyces coelicolor synthesizes three Nar enzymes that contribute to maintenance of a membrane potential when either the mycelium or the spores become hypoxic or anoxic. No growth occurs under such conditions but the bacterium survives the lack of O₂ by remaining metabolically active; reducing nitrate is one means whereby this process is aided. Nar1 is exclusive to spores, Nar2 to vegetative mycelium and Nar3 to stationary-phase mycelium, each making a distinct contribution to energy conservation. While Nar2 and Nar3 appear to function like conventional menaquinol oxidases, unusually, Nar1 is completely dependent for its activity on a cytochrome bcc-aa ₃ oxidase supercomplex. This suggest that electrons within this supercomplex are diverted to Nar1 during O₂ limitation. Receiving electrons from this supercomplex potentially allows nitrate reduction to be coupled to the Q-cycle of the cytochrome bcc complex. This modification likely improves the efficiency of energy conservation, extending longevity of spores under O₂ limitation. Knowledge gained on the bioenergetics of NO₃ ^- respiration in the actinobacteria will aid our understanding of how many microorganisms survive under conditions of extreme nutrient and energy restriction.

Purified F-ATP synthase forms a Ca2+-dependent high-conductance channel matching the mitochondrial permeability transition pore

The molecular identity of the mitochondrial megachannel (MMC)/permeability transition pore (PTP), a key effector of cell death, remains controversial. By combining highly purified, fully active bovine F-ATP synthase with preformed liposomes we show that Ca²⁺ dissipates the H⁺ gradient generated by ATP hydrolysis. After incorporation of the same preparation into planar lipid bilayers Ca²⁺ elicits currents matching those of the MMC/PTP. Currents were fully reversible, were stabilized by benzodiazepine 423, a ligand of the OSCP subunit of F-ATP synthase that activates the MMC/PTP, and were inhibited by Mg²⁺ and adenine nucleotides, which also inhibit the PTP. Channel activity was insensitive to inhibitors of the adenine nucleotide translocase (ANT) and of the voltage-dependent anion channel (VDAC). Native gel-purified oligomers and dimers, but not monomers, gave rise to channel activity. These findings resolve the long-standing mystery of the MMC/PTP and demonstrate that Ca²⁺ can transform the energy-conserving F-ATP synthase into an energy-dissipating device.

The molecular identity of the mitochondrial megachannel (MMC)/permeability transition pore (PTP), a key effector of cell death, remains controversial. Here authors demonstrate that the membrane embedded bovine F-ATP synthase elicits Ca2 + -dependent currents matching those of the MMC/PTP.

Cyclosporin A Increases Mitochondrial Buffering of Calcium: An Additional Mechanism in Delaying Mitochondrial Permeability Transition Pore Opening

Regulation of mitochondrial free Ca²⁺ is critically important for cellular homeostasis. An increase in mitochondrial matrix free Ca²⁺ concentration ([Ca²⁺]_m) predisposes mitochondria to opening of the permeability transition pore (mPTP). Opening of the pore can be delayed by cyclosporin A (CsA), possibly by inhibiting cyclophilin D (Cyp D), a key regulator of mPTP. Here, we report on a novel mechanism by which CsA delays mPTP opening by enhanced sequestration of matrix free Ca²⁺. Cardiac-isolated mitochondria were challenged with repetitive CaCl₂ boluses under Na⁺-free buffer conditions with and without CsA. CsA significantly delayed mPTP opening primarily by promoting matrix Ca²⁺ sequestration, leading to sustained basal [Ca²⁺]_m levels for an extended period. The preservation of basal [Ca²⁺]_m during the CaCl₂ pulse challenge was associated with normalized NADH, matrix pH (pH_m), and mitochondrial membrane potential (ΔΨ_m). Notably, we found that in PO₄³⁻ (P_i)-free buffer condition, the CsA-mediated buffering of [Ca²⁺]_m was abrogated, and mitochondrial bioenergetics variables were concurrently compromised. In the presence of CsA, addition of P_i just before pore opening in the P_i-depleted condition reinstated the Ca²⁺ buffering system and rescued mitochondria from mPTP opening. This study shows that CsA promotes P_i-dependent mitochondrial Ca²⁺ sequestration to delay mPTP opening and, concomitantly, maintains mitochondrial function.

Activity of Spore-Specific Respiratory Nitrate Reductase 1 of Streptomyces coelicolor A3(2) Requires a Functional Cytochrome bcc-aa 3 Oxidase Supercomplex

Spores have strongly reduced metabolic activity and are produced during the complex developmental cycle of the actinobacterium Streptomyces coelicolor Resting spores can remain viable for decades, yet little is known about how they conserve energy. It is known, however, that they can reduce either oxygen or nitrate using endogenous electron sources. S. coelicolor uses either a cytochrome bd oxidase or a cytochrome bcc-aa ₃ oxidase supercomplex to reduce oxygen, while nitrate is reduced by Nar-type nitrate reductases, which typically oxidize quinol directly. Here, we show that in resting spores the Nar1 nitrate reductase requires a functional bcc-aa ₃ supercomplex to reduce nitrate. Mutants lacking the complete qcr-cta genetic locus encoding the bcc-aa ₃ supercomplex showed no Nar1-dependent nitrate reduction. Recovery of Nar1 activity was achieved by genetic complementation but only when the complete qcr-cta locus was reintroduced to the mutant strain. We could exclude that the dependence on the supercomplex for nitrate reduction was via regulation of nitrate transport. Moreover, the catalytic subunit, NarG1, of Nar1 was synthesized in the qcr-cta mutant, ruling out transcriptional control. Constitutive synthesis of Nar1 in mycelium revealed that the enzyme was poorly active in this compartment, suggesting that the Nar1 enzyme cannot act as a typical quinol oxidase. Notably, nitrate reduction by the Nar2 enzyme, which is active in growing mycelium, was not wholly dependent on the bcc-aa ₃ supercomplex for activity. Together, our data suggest that Nar1 functions together with the proton-translocating bcc-aa ₃ supercomplex to increase the efficiency of energy conservation in resting spores.IMPORTANCE Streptomyces coelicolor forms spores that respire with either oxygen or nitrate, using only endogenous electron donors. This helps maintain a membrane potential and, thus, viability. Respiratory nitrate reductase (Nar) usually receives electrons directly from reduced quinone species; however, we show that nitrate respiration in spores requires a respiratory supercomplex comprising cytochrome bcc oxidoreductase and aa ₃ oxidase. Our findings suggest that the Nar1 enzyme in the S. coelicolor spore functions together with the proton-translocating bcc-aa ₃ supercomplex to help maintain the membrane potential more efficiently. Dissecting the mechanisms underlying this survival strategy is important for our general understanding of bacterial persistence during infection processes and of how bacteria might deal with nutrient limitation in the natural environment.

Mitochondrial F-ATP Synthase and Its Transition into an Energy-Dissipating Molecular Machine

The mitochondrial F-ATP synthase is the principal energy-conserving nanomotor of cells that harnesses the proton motive force generated by the respiratory chain to make ATP from ADP and phosphate in a process known as oxidative phosphorylation. In the energy-converting membranes, F-ATP synthase is a multisubunit complex organized into a membrane-extrinsic F₁ sector and a membrane-intrinsic F_O domain, linked by central and peripheral stalks. Due to its essential role in the cellular metabolism, malfunction of F-ATP synthase has been associated with a variety of pathological conditions, and the enzyme is now considered as a promising drug target for multiple disease conditions and for the regulation of energy metabolism. We discuss structural and functional features of mitochondrial F-ATP synthase as well as several conditions that partially or fully inhibit the coupling between the F₁ catalytic activities and the F_O proton translocation, thus decreasing the cellular metabolic efficiency and transforming the enzyme into an energy-dissipating structure through molecular mechanisms that still remain to be defined.

Redox Equivalents and Mitochondrial Bioenergetics

Mitochondrial energy metabolism depends upon high-flux and low-flux electron transfer pathways. The former provide the energy to support chemiosmotic coupling for oxidative phosphorylation. The latter provide mechanisms for signaling and control of mitochondrial functions. Few practical methods are available to measure rates of individual mitochondrial electron transfer reactions; however, a number of approaches are available to measure steady-state redox potentials (E _h) of donor/acceptor couples, and these can be used to gain insight into rate controlling reactions as well as mitochondrial bioenergetics. Redox changes within the respiratory electron transfer pathway are quantified by optical spectroscopy and measurement of changes in autofluorescence. Low-flux pathways involving thiol/disulfide redox couples are measured by redox Western blot and mass spectrometry-based redox proteomics. Together, the approaches provide the opportunity to develop integrated systems biology descriptions of mitochondrial redox signaling and control mechanisms.

The prediction of intermolecular proton-transfer of guanine-cytosine base pair under the influence of fragments from decomposed MOFs

Metal-organic frameworks (MOFs) can be decomposed into various fragments, including negative/positive charges, Zn⁺ or Cu²⁺ when used as drug delivery materials. To evaluate the safety of MOFs, different mechanisms of intermolecular proton-transfer in guanine-cytosine (GC) base pair under the influence of such fragments were investigated by density functional theory methods. In a vacuum, calculation results show that an excess electron assists proton transfer in the anionic GC radical, and a hole assists proton transfer in the cationic GC radical with small energy barriers. The mechanism for Zn⁺-GC transfer is that the located hole assists proton transfer from G to C. All proton-transfers of Cu²⁺-GC become spontaneous with stable proton-transferred structures, and the driving force is the Cu²⁺ due to its electrostatic and oxidative effects. However, in a micro-water environment, the average energy barrier of all proton-transfer processes increases by 2.8 kcal mol^-1 because of the redistribution of charges. Water molecules play a very important role in buffering, and the influence of fragments on intermolecular proton-transfer processes of GC is reduced.

Effects of unsaturation of long-chain fatty acids on rumen protozoal engulfment and microbial protein recycling in protozoa in vitro

The present study investigated the effects of long-chain fatty acids with different degrees of unsaturation on rumen protozoal engulfment and microbial protein recycling by protozoa in vitro. The seven experimental treatments included stearic acid (C18:0, Group A), oleic acid (C18:1, n-9, Group B), linoleic acid (C18:2, n-6, Group C), α-linoleic acid (C18:3, n-3, Group D), arachidonic acid (C20:4, n-6, Group E), eicosapentaenoic acid (C20:5, n-3, Group F) and calcium palmitate (C16:0, control group, G), each being included at 3% (w/w) in the total culture substrate containing starch, xylan, araban, glucan, mannan, cellulose, pectin, lignin, urea and casein. Three goats fitted with rumen cannula were used to provide rumen fluid. The incubation medium was collected for the measurement of engulfing rate of bacteria by protozoa and microbial biomass after 24 h of in vitro incubation. The results showed that the bacterial density of Group D (5.75 × 109 cells/mL) was significantly higher than that of Groups A, B, E, F and G (P &lt; 0.05), but that of the control (Group G) as well as those of Groups A and B were lower than those of Groups D and C (P &lt; 0.05). Similarly, the bacterial protein was the highest in Group D and the lowest in Group G. The number of bacteria engulfed by protozoa per millilitre were the highest in the Control group G (847 × 105 cells/(mL.h)) and the lowest in Group D (392 × 105 cells/(mL.h)). The recycling rate of bacterial cells was lowest in Group D (0.68%) and the recycling time of bacterial cells was the longest (147 h). The quantity of protein recycled was lowest in Group D and highest in Group G, which derived from the number of bacterial cells engulfed. Therefore, it was concluded that the effects of long-chain fatty acids on rumen microbial protein recycling and microbial protein synthesis mainly relate to their degree of unsaturation, with α-linoleic acid possessing a better ability to suppress bacterial-cell (by protozoa) and reduce protein yield.

Structural characterization of nucleotide 5'-triphosphates by infrared ion spectroscopy and theoretical studies

The molecular family of nucleotide triphosphates (NTPs), with adenosine 5'-triphosphate (ATP) as its best-known member, is of high biochemical importance as their phosphodiester bonds form Nature's main means to store and transport energy. Here, gas-phase IR spectroscopic studies and supporting theoretical studies have been performed on adenosine 5'-triphosphate, cytosine 5'-triphosphate and guanosine 5'-triphosphate to elucidate the intrinsic structural properties of NTPs, focusing on the influence of the nucleobase and the extent of deprotonation. Mass spectrometric studies involving collision induced dissociation showed similar fragmentation channels for the three studied NTPs within a selected charge state. The doubly charged anions exhibit fragmentation similar to the energy-releasing hydrolysis reaction in nature, while the singly charged anions show different dominant fragmentation channels, suggesting that the charge state plays a significant role in the favorability of the hydrolysis reaction. A combination of infrared ion spectroscopy and quantum-chemical computations indicates that the singly charged anions of all NTPs are preferentially deprotonated at their β-phosphates, while the doubly-charged anions are dominantly αβ-deprotonated. The assigned three-dimensional structure differs for ATP and CTP on the one hand and GTP on the other, in the sense that ATP and CTP show no interaction between nucleobase and phosphate tail, while in GTP they are hydrogen bonded. This can be rationalized by considering the structure and geometry of the NTPs where the final three dimensional structure depends on a subtle balance between hydrogen bond strength, flexibility and steric hindrance.

Green Rust: The Simple Organizing 'Seed' of All Life?

Korenaga and coworkers presented evidence to suggest that the Earth's mantle was dry and water filled the ocean to twice its present volume 4.3 billion years ago. Carbon dioxide was constantly exhaled during the mafic to ultramafic volcanic activity associated with magmatic plumes that produced the thick, dense, and relatively stable oceanic crust. In that setting, two distinct and major types of sub-marine hydrothermal vents were active: ~400 °C acidic springs, whose effluents bore vast quantities of iron into the ocean, and ~120 °C, highly alkaline, and reduced vents exhaling from the cooler, serpentinizing crust some distance from the heads of the plumes. When encountering the alkaline effluents, the iron from the plume head vents precipitated out, forming mounds likely surrounded by voluminous exhalative deposits similar to the banded iron formations known from the Archean. These mounds and the surrounding sediments, comprised micro or nano-crysts of the variable valence FeII/FeIII oxyhydroxide known as green rust. The precipitation of green rust, along with subsidiary iron sulfides and minor concentrations of nickel, cobalt, and molybdenum in the environment at the alkaline springs, may have established both the key bio-syntonic disequilibria and the means to properly make use of them-the elements needed to effect the essential inanimate-to-animate transitions that launched life. Specifically, in the submarine alkaline vent model for the emergence of life, it is first suggested that the redox-flexible green rust micro- and nano-crysts spontaneously precipitated to form barriers to the complete mixing of carbonic ocean and alkaline hydrothermal fluids. These barriers created and maintained steep ionic disequilibria. Second, the hydrous interlayers of green rust acted as engines that were powered by those ionic disequilibria and drove essential endergonic reactions. There, aided by sulfides and trace elements acting as catalytic promoters and electron transfer agents, nitrate could be reduced to ammonia and carbon dioxide to formate, while methane may have been oxidized to methyl and formyl groups. Acetate and higher carboxylic acids could then have been produced from these C1 molecules and aminated to amino acids, and thence oligomerized to offer peptide nests to phosphate and iron sulfides, and secreted to form primitive amyloid-bounded structures, leading conceivably to protocells.

Extracellular Potassium and Glutamate Interact To Modulate Mitochondria in Astrocytes

Astrocytes clear glutamate and potassium, both of which are released into the extracellular space during neuronal activity. These processes are intimately linked with energy metabolism. Whereas astrocyte glutamate uptake causes cytosolic and mitochondrial acidification, extracellular potassium induces bicarbonate-dependent cellular alkalinization. This study aimed at quantifying the combined impact of glutamate and extracellular potassium on mitochondrial parameters of primary cultured astrocytes. Glutamate in 3 mM potassium caused a stronger acidification of mitochondria compared to cytosol. 15 mM potassium caused alkalinization that was stronger in the cytosol than in mitochondria. While the combined application of 15 mM potassium and glutamate led to a marked cytosolic alkalinization, pH only marginally increased in mitochondria. Thus, potassium and glutamate effects cannot be arithmetically summed, which also applies to their effects on mitochondrial potential and respiration. The data implies that, because of the nonlinear interaction between the effects of potassium and glutamate, astrocytic energy metabolism will be differentially regulated.

Maturation of Cardiac Energy Metabolism During Perinatal Development

As one of the highest energy consumer organ in mammals, the heart has to be provided with a high amount of energy as soon as its first beats in utero. During the development of this organ, energy is produced within the cardiac muscle cell depending on substrate availability, oxygen pressure and cardiac workload that drastically change at birth. Thus, energy metabolism relying essentially on carbohydrates in fetal heart is very different from the adult one and birth is the trigger of a profound maturation which ensures the transition to a highly oxidative metabolism depending on lipid utilization. To face the substantial increase in cardiac workload resulting from the growth of the organism during the postnatal period, the heart not only develops its capacity for energy production but also undergoes a hypertrophic growth to adapt its contractile capacity to its new function. This leads to a profound cytoarchitectural remodeling of the cardiomyocyte which becomes a highly compartmentalized structure. As a consequence, within the mature cardiac muscle, energy transfer between energy producing and consuming compartments requires organized energy transfer systems that are established in the early postnatal life. This review aims at describing the major rearrangements of energy metabolism during the perinatal development.