Light-scattering and absorption effects caused by addition of adenosine diphosphate to rat-heart-muscle sarcosomes

The mitochondrial permeability transition pore: an evolving concept critical for cell life and death

In this review, we summarize current knowledge of perhaps one of the most intriguing phenomena in cell biology: the mitochondrial permeability transition pore (mPTP). This phenomenon, which was initially observed as a sudden loss of inner mitochondrial membrane impermeability caused by excessive calcium, has been studied for almost 50 years, and still no definitive answer has been provided regarding its mechanisms. From its initial consideration as an in vitro artifact to the current notion that the mPTP is a phenomenon with physiological and pathological implications, a long road has been travelled. We here summarize the role of mitochondria in cytosolic calcium control and the evolving concepts regarding the mitochondrial permeability transition (mPT) and the mPTP. We show how the evolving mPTP models and mechanisms, which involve many proposed mitochondrial protein components, have arisen from methodological advances and more complex biological models. We describe how scientific progress and methodological advances have allowed milestone discoveries on mPTP regulation and composition and its recognition as a valid target for drug development and a critical component of mitochondrial biology.

Differences in forward angular light scattering distributions between M1 and M2 macrophages

The ability to distinguish macrophage subtypes noninvasively could have diagnostic potential in cancer, atherosclerosis, and diabetes, where polarized M1 and M2 macrophages play critical and often opposing roles. Current methods to distinguish macrophage subtypes rely on tissue biopsy. Optical imaging techniques based on light scattering are of interest as they can be translated into biopsy-free strategies. Because mitochondria are relatively strong subcellular light scattering centers, and M2 macrophages are known to have enhanced mitochondrial biogenesis compared to M1, we hypothesized that M1 and M2 macrophages may have different angular light scattering profiles. To test this, we developed an in vitro angle-resolved forward light scattering measurement system. We found that M1 and M2 macrophage monolayers scatter relatively unequal amounts of light in the forward direction between 1.6 deg and 3.2 deg with M2 forward scattering significantly more light than M1 at increasing angles. The ratio of forward scattering can be used to identify the polarization state of macrophage populations in culture.

Photon correlation spectroscopy of brain mitochondrial populations: Application to traumatic brain injury

Mitochondrial dysfunction and pathology that contribute to a host of neurodegenerative diseases are deduced from changes in ultrastructure, routinely examined by a host of optical techniques. We adapted the technique of photon correlation spectroscopy (PCS) to evaluate calcium-induced structural alterations in isolated viable cortical and hippocampal mitochondria. In detecting calcium-induced reductions in light intensity, PCS was more sensitive than absorbance across varying calcium concentrations. Mitochondrial populations encompass a broad distribution of sizes, confirmed by ultrastructural profiles, both which remain unaffected by calcium exposure. Cortical and hippocampal populations show fractional calcium-induced reductions in light scatter compared to subsequent maximal alamethicin-induced reductions. Although reductions in light scatter (refractive index) have been interpreted as mitochondrial swelling, PCS quantification of the mean mitochondrial radius demonstrates that mitochondrial size is unaffected by calcium exposure, but not alamethicin. Likewise, the population distribution histograms remain stable with calcium exposure, but shift to larger radii after alamethicin exposure. Furthermore, hippocampal mitochondrial populations from a neurodegenerative model of traumatic brain injury, lateral fluid percussion, demonstrate greater calcium-induced reductions in scatter intensity, which are associated with an initial population of large mitochondria becoming smaller. The disparate responses to calcium and subsequent alamethicin of mitochondria at 3 and 24 h after injury attest to an acute disruption of membrane permeability in mitochondria from injured brain. PCS provides quantitative indices of refractive index and size in isolated mitochondrial populations, aiding the evaluation of mitochondria in degenerative diseases.

SIZE AND SHAPE TRANSFORMATIONS CORRELATED WITH OXIDATIVE PHOSPHORYLATION IN MITOCHONDRIA. I. SWELLING-SHRINKAGE MECHANISMS IN INTACT MITOCHONDRIA

Two types of swelling-shrinkage change manifested by isolated mammalian heart mitochondria have been studied. One type, designated as phase I or "low amplitude" swelling-shrinkage, is estimated to lead to changes in mitochondrial volume of 20 to 40 per cent, to changes in light scattering of about 30 per cent, and to changes in viscosity. These physical changes in mitochondria are brought about rapidly and reversibly by normal reactants of the respiratory chain. Their speed, specificity, and reversibility indicate that they are closely geared to the normal function of the respiratory chain and are a true reflection of a mechanochemical coupling process characteristic of the physiology of mitochondria. A second type of swelling-shrinkage mechanism, designated as phase II or "high amplitude," leads to changes in light scattering, viscosity, and mitochondrial volume which, frequently but not always, are of higher magnitude than the phase I type. Phase II swelling-shrinkage seems to be only partly under the control of the respiratory chain. Prior to the completion of phase II swelling, a stepwise loss of mitochondrial function can be identified, such as changes in the rate of substrate utilization and loss of respiratory control. Reversal of this type of swelling cannot be effected if the swelling change reaches a steady state. This type of swelling may provide cells with a mechanism for destroying mitochondrial substance.

CALCIUM ION ACCUMULATION AND VOLUME CHANGES OF ISOLATED LIVER MITOCHONDRIA. REVERSAL OF CALCIUM ION-INDUCED SWELLING

1. The excessive accumulation of Ca(2+) by mitochondria suspended in an iso-osmotic buffered potassium chloride medium containing oxidizable substrate and phosphate led to extensive swelling and release of accumulated Ca(2+) from the mitochondria. When the Ca(2+) was removed from the medium by chelation with ethylene glycol bis(aminoethyl)tetra-acetate, the swelling was reversed in a respiration-dependent contraction. The contracted mitochondria were shown to have regained some degree of respiratory control. 2. The respiration-dependent contraction could be supported by electron transport through a restricted portion of the respiratory chain, and by substrates donating electrons at different levels in the respiratory chain. 3. Respiratory inhibitors appropriate to the substrate present completely inhibited the contraction. Uncoupling agents, and the inhibitors oligomycin and atractyloside, were without effect. 4. When the reversal of swelling had been prevented by respiratory inhibitors, the addition of ATP induced a contraction of the mitochondria. In the absence of added chelating agent the contraction was very slow. The ATP-induced contraction was completely inhibited by oligomycin and atractyloside, was incomplete in the presence of uncoupling agents and was unaffected by respiratory inhibitors. 5. The relationship between the energy requirements of respiration-dependent contraction and the requirements of ion transport and other contractile systems are discussed.

RESPIRATORY AND ELECTRICAL RESPONSES TO LIGHT SIMULATION IN THE RETINA OF THE FROG

Isolated retinas from frogs' eyes were preserved in a circulating medium; transretinal electrical potential and ultraviolet absorbancy were monitored. In response to visible stimulation, changes in absorbancy were observed which correlate with the c-wave of the electroretinogram. They are tentatively identified as cyclic oxidations of pyridine nucleotides reflecting the energy expenditure associated with evoked neuronal activity.

Duramycin effects on the structure and function of heart mitochondria. I. Structural alterations and changes in membrane permeability

The polypeptide antibiotic duramycin has been reported to interact specifically with two lipids: phosphatidylethanolamine (PE) and monogalactosyldiacylglycerol (Navarro et al. (1985) Biochemistry 24, 4645-4650). PE is a major component of mitochondrial membranes. Duramycin was used to examine the role of PE in maintenance of mitochondrial structure and membrane permeability properties with the following results: (1) Duramycin addition to isolated rat heart mitochondria produced abrupt organelle contraction which was followed, depending on composition of the suspending medium, by pronounced swelling. The most notable morphological effect of the antibiotic was ruffling or crenelation of the outer membrane, which resulted ultimately in its separation from the inner membrane. (2) Low concentrations (less than 5 microM) of the antibiotic selectively increased the permeability of the mitochondrial inner membrane to cations and small solutes. This effect was blocked by atractyloside, a highly specific inhibitor of the adenine nucleotide translocator, by palmitoyl coenzyme A, by N-ethylmaleimide, and by AMP, ADP and ATP but not GDP or GTP, implicating the adenine nucleotide translocator in the selective permeability increase. (3) Higher concentrations of duramycin induced a more generalized permeability increase which was not subject to inhibition by compounds capable of interacting with the adenine nucleotide translocator.

Influence of the conformational state on the isoelectric points of rat brain synaptosomes, mitochondria and mitoplasts

The isoelectric points of rat brain synaptosomes, mitochondria and mitoplasts have been determined by using different charged two-phase systems containing dextran and poly(ethylene glycol). The cross-partition diagrams of these organelles show isoelectric points at pH 4.1, 4.5 and 4.7, respectively. The influence of the conformational state of mitochondrial membranes upon their partition in two-phase systems has been studied. Shrunk mitoplasts showed a large change in their partition behavior as reflected by an increased affinity for the lower dextran phase, while shrinkage of mitochondria did not affect their partition. Shrunk mitoplasts showed the same isoelectric point of pH 4.7 as swollen mitoplasts, which indicates that no charge changes occurred on the outer side of the inner mitochondrial membrane during shrinkage of mitoplasts.

Ultrastructural studies of beef heart mitochondria. 3. The inequality of gross morphological change and oxidative phosphorylation

The relationships between membranes and intramembrane compartments of isolated heart mitochondria are inadequately defined to express the induced morphological changes associated with the structural organization. The inner membrane and matrix are the major structural entities which undergo transformation upon alteration of metabolism or incubation conditions. To better express these morphological changes within a mitochondrion, two inner membranes plus enclosed matrix are defined as an inmerix (plural inmerices). Three general morphological forms of mitochondria can be distinguished by the size and shape of inmerices. These are distended, condensed, and coalesced inmerixal configurations. Hypotonic conditions and P(i) in isotonic sucrose generate distended configurations. This P(i) distention is apparently dependent on utilization of energy. It does not occur under anaerobic conditions. Oxidizable substrates generate condensed configurations. ADP and dADP generate coalesced configurations and stop formation of condensed and distended inmerixal configurations in the absence of inhibitors. ADP coalescence is apparently not dependent on an energy input. It occurs under aerobic and anaerobic conditions, and in isotonic and hypotonic media. Atractyloside completely inhibits the effects of ADP on inmerixal membranes whereas oligomycin does not. Distention by P(i) is unaffected by the two inhibitors. Distended inmerices, without added P(i) (12 mM and 62 mM sucrose), are coalesced by ADP. These studies indicate that coalescence of inmerixal membranes probably reflects the consequences of specific stoichiometric binding or translocation of adenine nucleotides.

A fluorescence probe of energy-dependent structure changes in fragmented membranes

The reaction of the fluorochrome, 8-anilino-1-naphthalene-sulfonic acid (ANS), with fragmented membranes from beef heart mitochondria has been studied. ANS fluorescence is found to be enhanced 25-fold on binding to the membrane fragments in the absence of energy conservation, and this enhancement is increased to 35-fold in the membrane energized by substrate plux oxygen. The fluorescence of bound ANS depends upon the energy state of the membrane fragments, as indicated by the effects of ATP, substrates of the respiratory chain, oligomycin, and uncouplers. It is concluded that the changes of ANS fluorescence indicate structural changes of the mitochondrial membrane associated with energy conservation. The time course of energization is readily followed by ANS, and has a half-time of two seconds at 26 degrees .

The reactivity of haemoproteins and cytochromes

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Ultrastructural bases for metabolically linked mechanical activity in mitochondria. I. Reversible ultrastructural changes with change in metabolic steady state in isolated liver mitochondria

By means of a new "quick-sampling" method, micropellets of mouse liver mitochondria were rapidly prepared for electron microscopy during the recording of steady state metabolism. Reversible ultrastructural changes were found to accompany change in metabolic steady states. The most dramatic reversible ultrastructural change occurs when ADP is added to systems in which only phosphate acceptor is deficient, i.e., during the State IV to State III transition as defined by Chance and Williams. After 15 min in State IV, mitochondria display an "orthodox" ultrastructural appearance as is usually observed after fixation within intact tissue. On transition to State III, a dramatic change in the manner of folding of the inner membrane takes place. In addition, the electron opacity of the matrix increases as the volume of the matrix decreases, but total mitochondrial volume does not appear to change during this transition. This conformation is called "condensed." Isolated mitochondria were found to oscillate between the orthodox and condensed conformations during reversible transitions between State III and State IV. Various significant ultrastructural changes in mitochondria also occur during transitions in other functional states, e.g., when substrate or substrate and acceptor is made limiting. Internal structural flexibility is discussed with respect to structural and functional integrity of isolated mitochondria. Reversible changes in the manner of folding of the inner membrane and in the manner of packing of small granules in the matrix as respiration is activated by ADP represent an ultrastructural basis for metabolically linked mechanical activity in tightly coupled mitochondria.

Reaction of oxygen with the respiratory chain in cells and tissues

This paper considers the way in which the oxygen reaction described by Dr. Nicholls and the ADP control reactions described by Dr. Racker could cooperate to establish a purposeful metabolic control phenomenon in vivo. This has required an examination of the kinetic properties of the respiratory chain with particular reference to methods for determinations of oxygen affinity (K(m)). The constant parameter for tissue respiration is k(1), the velocity constant for the reaction of oxygen with cytochrome oxidase. Not only is this quantity a constant for a particular tissue or mitochondria; it appears to vary little over a wide range of biological material, and for practical purposes a value of 5 x 10(7) at 25 degrees close to our original value (20) is found to apply with adequate accuracy for calculation of K(m) for mammalia. The quantity which will depend upon the tissue and its metabolic state is the value of K(m) itself, and K(m) may be as large as 0.5 microM and may fall to 0.05 microM or less in resting, controlled, or inhibited states. The control characteristic for ADP may depend upon the electron flux due to the cytochrome chain (40); less ADP is required to activate the slower electron transport at lower temperatures than at higher temperatures. The affinity constants for ADP control appear to be less dependent upon substrate supplied to the system. The balance of ADP and oxygen control in vivo is amply demonstrated experimentally and is dependent on the oxygen concentration as follows. In the presence of excess oxygen, control may be due to the ADP or phosphate (or substrate), and the kinetics of oxygen utilization will be independent of the oxygen concentration. As the oxygen concentration is diminished, hemoglobin becomes disoxygenated, deep gradients of oxygen concentration develop in the tissue, and eventually cytochrome oxidase becomes partially and then completely reduced. DPN at this point will become reduced and the electron flow diminished. The rate of ATP production falls and energy conservation previously under the control of the ADP concentration will now be controlled by the diffusion of oxygen to the respiratory enzymes in the mitochondria. Under these conditions the rate of reaction of cytochrome oxidase with oxygen and the reaction of cytochromes with one another become of key importance. The rise of ADP and the depletion of energy reserves evoke glycolytic activity, and failure of biological function may result.