https://deepblue.lib.umich.edu/bitstream/2027.42/30145/1/0000522.pdf

Cardiolipins and biomembrane function

Mitochondrial oxidative phosphorylation changes in the life span. Molecular aspects and physiopathological implications

Summary

1.Because the calcium (Ca) ion is intimately associated with so many biochemical and physiological phenomena, it is fundamental to understand how intracellular Ca is maintained and controlled. This review draws attention to the vital role played by mitochondria in controlling intracellular Ca and describes how transport of the ion into and out of mitochondria may itself be controlled.



2.The heterogeneous distribution of Ca is a property of most, if not all cells. This arises because the ion binds strongly to a variety of biological compounds, especially those containing oxyanions, which themselves have a heterogeneous distribution in cells, but mostly because of the existence in the cell of specific Ca-ion transport systems.



3.Although the concentration of total Ca in the cell may be quite high, a very large proportion of it is bound and non-diffusible; a small fraction is diffusible but unionized. The proportion of Ca that is ionized is probably much less than I% of the total



4.The mechanisms by which Ca is transported into and out of the mitochondrial matrix are discussed. Inward movement of the ion occurs in response to the membrane potential (negative inside) generated by respiration. The process is carrier-mediated and exhibits characteristics such as substrate specificity, high affinity for Ca, satur-ability, cooperativity, stimulation by permeant anions and is specifically inhibited by low concentrations of Ruthenium Red and lanthanum. The properties of the Ca carrier are geared therefore to facilitate rapid inward movement of Ca into the mitochondria. Such a carrier system is found in mitochondria isolated from a wide variety of tissues and species.



5.Ionized Ca appears not to be distributed across the inner mitochondrial membrane according to the Nernst equation, so the possibility exists that the ion is transported as Ca/H+ antiport or as Ca/anion symport. Alternatively, an efflux system coupled to inward movement of a cation may serve to prevent the [Ca ion]in/[Ca ion]out from attaining equilibrium. These components together contribute to a Ca-translocation cycle that permits Considerable flexibility in the overall control of Ca flux.



6.Evidence for Ca cycling in mitochondria is presented and the influence of physiological agents such as Mg, phosphoenolpyruvate, inorganic phosphate and adenine nucleotides, on the influx and efflux components are discussed in some detail. Moreover, various hormones administered in vivo are able to induce changes in mitochondrial Ca cycling. One important feature that emerges from this collection of data is that the ability of mitochondria to retain Ca is associated with their ability to retain also their adenine-nucleotide complement.



7.Various lines of research provide convincing evidence in support of the view that mitochondria play a major role in controlling cell Ca in vivo. Especially significant are the observations that the ‘activity’ of mitochondrial Ca transport can change during development in both insect and mammalian tissue, can depend on the hormonal status of the tissue and undergoes a permanent change in certain tumour cells.



8.Finally, consideration is given as to how the mitochondrial Ca transport system is able to modify Ca-sensitive enzyme activities by regulating the Ca concentration in specific environments. Some biological activities that might be susceptible to such control are discussed.

Mitochondria and the control of intracellular calcium.

Ca2+ signaling in mitochondria is important to tune mitochondrial function to a variety of extracellular stimuli. The main mechanism is Ca2+ entry in mitochondria via the Ca2+ uniporter followed by...

Mitochondrial transporters as novel targets for intracellular calcium signaling

Publisher Summary This chapter discusses the carrier system responsible for transporting calcium across the inner membrane of mitochondria as well as difficulties associated with the technology involved in the analyses and their solutions to overcome. The mitochondrial calcium transport system is a primary mechanism used by cells to modify the intracellular distribution of calcium. Mitochondria isolated from a range of tissues and species possess a specific carrier in their inner membrane whose function is to rapidly transport calcium inwardly and outwardly against electrochemical and metabolite concentration gradients. The major role of mitochondrial calcium transport is to control cell metabolism by modification of the ionic environment

Mitochondrial Calcium Transport

A new method was devised for the isolation of foetal and neonatal rat lvier mitochondria, giving higher yields than conventional methods. 2. During development from the perinatal period to the mature adult, the ratio of cytochrome oxidase/succinate-cytochrome c reductase changes. 3. The inner mitochondrial membrane of foetal liver mitochondria possesses virtually no osmotic activity; the permeability to sucrose decreases with increasing developmental age. 4. Foetal rat liver mitochondria possess only marginal respiratory control and do not maintain Ca2+-induced respiration; they also swell in respiratory-control medium in the absence of substrate. ATP enhances respiratory control and prevents swelling, adenylyl imidodiphosphate, ATP+atractyloside enhance the R.C.I. (respiratory control index), Ca2+-induced respiratory control and prevent swelling, whereas GTP and low concentrations of ADP have none of these actions. It is concluded that the effect of ATP depends on steric interaction with the inner mitochondrial membrane. 5. When 1-day pre-partum foetuses are obtained by Caesarean section and maintained in a Humidicrib for 90 min, mitochondrial maturation is "triggered", so that their R.C.I. is enhanced and no ATP is required to support Ca2+-dependent respiratory control or to inhibit mitochondrial swelling. 6. It is concluded that foetal rat liver mitochondria in utero do not respire, although they are capable of oxidative phosphorylation in spite of their low R.C.I. The different environmental conditions which the neonatal rat encounters ex utero enable the hepatic mitochondria to produce ATP, which interacts with the inner mitochondrial membrane to enhance oxidative phosphorylation by an autocatalytic mechanism.

The maturation of the inner membrane of foetal rat liver mitochondria.

1. Two populations of morphologically intact mitochondria were isolated from embryonic, neonatal and adult chick liver by isopycnic centrifugation. 2. The protein/phospholipid ratio of the total mitochondrial fraction, the low-density mitochondria (B2, d1.176) and the high-density mitochondria (B3, d1.206) did not differ significantly. 3. During development there is a marked increase in the B2 fraction in relation to the B3 fraction. 4. Cytochrome oxidase and malate dehydrogenase activities as well as respiratory control increased during the embryonic development of the chick, though their rates of increase were not correlated. 5. In the three different embryonic stages that were investigated, as well as in the neonatal and adult chick, the protein/lipid as well as the protein/phospholipid ratio stayed constant and showed no progressive increase, as had been previously reported. 6. It was shown that forces greater than 18400gav. for 2h have to be used before chick liver mitochondria reach isopycnic equilibrium. 7. As for rat liver mitochondria, the constant protein/phospholipid ratio of the B2 and B3 fractions and their apparent morphological intactness leads one to conclude that the matrix space of B2 mitochondria is inaccessible to sucrose, whereas B3 mitochondria possess an inner membrane that is permeable to sucrose.

Changes in the proportions of two mitochondrial populations during the development of embryonic chick liver

1. The structural-protein component of microsomal membranes was isolated by three separate methods. Analysis by polyacrylamide-gel electrophoresis indicated that the microsomal structural component is made up of a heterogeneous group of proteins. These proteins were further characterized by their phospholipid-binding capacity. The electrophoretic patterns of microsomal structural proteins were found to differ significantly from those of mitochondrial structural proteins. 2. The reticulosomal fraction was also characterized by electrophoresis with reference to total microsomal proteins, microsomal structural proteins and ribosomal proteins. The reticulosomes gave an electrophoretic pattern significantly different from those of the other three preparations examined. It is suggested that reticulosomes consist largely of enzymic proteins of the endoplasmic reticulum.

/pdf/the-composition-of-rat-liver-microsomes-the-structural-1t51yuyomc.pdf

The composition of rat liver microsomes. The structural proteins of rat liver microsomes.

A major difficulty in studying quantitative changes in free and membrane-bound ribosomes in a tissue under different physiological conditions is that membrane-bound ribosomes are not usually recovered quantitatively in a conventional microsomal fraction. This problem was resolved for developing chick liver by determining the conditions for the isolation of a microsomal fraction containing the highest practicable yield of rough vesicles, and then separating it into free-ribosome- and rough-vesicle-containing fractions. With the aid of a marker enzyme for the microsomal membranes and the RNA content of the recovered membrane-bound ribosomes, it was possible to correct for the recovery of rough vesicles and hence to determine the concentration of membrane-bound ribosomes in the homogenate. Despite the fact that morphological studies have suggested that most of the cellular ribosomes are not bound to membrane in chick liver cells at the earliest developmental age studied (6 days of egg incubation), 49% of the total ribosomes were found to be membrane-bound by using the new fractionation technique. This fraction increased (to 66%) during development. The discrepancy between the cell-fractionation and morphological approaches could not be attributed to artifacts of the separation method but rather to difficulties inherent in the morphological approach.

/pdf/changes-in-free-and-membrane-bound-ribosomes-during-the-52y6apbyqv.pdf

J. K. Pollak

Papers

The maturation of the inner membrane of foetal rat liver mitochondria.

Changes in the proportions of two mitochondrial populations during the development of embryonic chick liver

The composition of rat liver microsomes. The structural proteins of rat liver microsomes.

Changes in free and membrane-bound ribosomes during the development of chick liver