Mitochondrial ultrastructure and volume during swelling

Ultrastructural aspects of preeclampsia. II. Mitochondrial changes

Biopsy specimens were obtained under direct vision at the time of cesarean section from 47 patients (35 with preeclampsia and 12 normotensive patients) and from four women with cesarean section hysterectomies (all normotensive) as an extension of previous work. Tissues were obtained from the myometrium near the placental bed and from the opposite side of the uterus. Skin biopsies were also obtained from eight women with preeclampsia and liver biopsies were obtained from two patients with acute microvesicular fatty change of pregnancy (one with and one without concomitant preeclampsia). Specimens were examined histologically and by electron microscopy. Mitochondrial changes in small vessels, principally venules, in myometrial smooth muscle, myometrial interstitial cells, circulating leukocytes, epidermal and dermal cells, and hepatocytes were examined and compared between women with preeclamptic and normotensive pregnancies. These findings were then compared with mitochondria from 500 biopsies over the same 3-year interval to assess the possible role of delay in tissue fixation. There were 12 other biopsies from nonpregnant women of childbearing age. As further control on artifact, other specimens were initially sampled immediately in the operating room and then serially for up to 2 hours later. Artifact as a basis for the mitochondrial changes was ruled out by these procedures. Normal mitochondria undergo a morphologic conformational sequence with physiologic changes in substrate, oxygen consumption, adenosine diphosphate, and respiratory rate. The mitochondria of preeclamptic tissues show a central disruption that is outside this normal sequence or cycle. This disruption occurs more often and is more severe in preeclampsia than in normotensive pregnancies. In addition, the hypertrophic smooth muscle of the pregnant uterus has a complex of cytoplasmic organelles in a paranuclear location, usually apical, that contains a variable mixture of glycogen, the Golgi apparatus, endoplasmic reticulum, mitochondria, and small unidentified microvesicles. This complex has the location and appearance suggestive of a myometrial "power pack" of significance in metabolism and contraction. The presence of similar mitochondrial changes in a limited sample of nonuterine tissues is suggestive of a systemic metabolic disorder as an important feature of preeclampsia.

Ion transport in rat liver mitochondria: the effect of the incubation medium osmolarity

A decrease in the incubation medium osmolarity from 320 to 120 mosM reverses the pH dependence of K+ efflux from rat liver mitochondria. The K+ efflux is no longer inhibited by oligomycin and a free radical scavenger butylhydroxytoluene. At 320 mosM, the addition of carbonyl cyanide 3-chlorophenylhydrazone (CCCP) accelerates the K+ efflux, while EGTA inhibits it. At 120 mosM these CCCP and EGTA effects are reversed. In either case the K+ efflux is inhibited by Mg2+. The decrease in osmolarity changes the ruthenium red-insensitive Ca2+ efflux in the same manner. It has thus been shown that the modification of the mitochondrial structure by changing the incubation medium osmolarity results in a qualitative alteration of the systems regulating the K+ and Ca2+ effluxes.

Ca2+ release from energetically coupled tumor mitochondria

A Na+/Ca2+ exchange activity for Ca2+ efflux has been identified in isolated Ehrlich ascites tumor mitochondria. Further, under conditions favoring cycling of Ca2+ across the mitochondrial inner membrane, extramitochondrial [Ca2+] also was shown to be Na+-dependent. The Na+/Ca2+ exchange showed sigmoidal kinetics with a mean (+/-SD) [Na+] required for half maximal stimulation of Ca2+ efflux of 8.4 +/- 3.8 mM and a Hill coefficient of 1.6. Na+/Ca2+ exchange was very sensitive to inhibition by the Ca2+ antagonist diltiazem (56% inhibition at 7.5 nmoles X mg protein-1) whereas a number of other compounds, including verapamil, nupercaine, and trifluoperazine were less effective in inhibiting Ca2+ efflux. These data demonstrate for the first time the presence of a pathway in tumor mitochondria for unidirectional Ca2+ efflux induced by Na+, and provide a mechanism for regulation of tumor intra- and extramitochondrial [Ca2+]. Results of the present study support the need for further study of intracellular Na+ and its role in regulation of Ca2+ homeostasis in tumor cells.

Structure-function relations between fatty acid oxidation and the mitochondrial inner-membrane--matrix region

Decreasing the osmolarity of the incubation media for rat liver mitochondria, by lowering the KCl or sucrose content, greatly increased the oxidation of palmitate, palmitoyl-CoA, palmitoyl-(-)-carnitine, octanoate and butyrate, but only slightly affected the oxidation of succinate, glutamate plus malate, and 3-hydroxybutyrate. Kinetic studies indicated that the increased rate of fatty acid oxidation commenced at the onset of incubation in the hypotonic media and remained relatively constant. This was accompanied by an increase in the 3-hydroxybutyrate: acetoacetate ratio, a higher rate of oxygen consumption, an increase in the extramitochondrial adenine-nucleotide phosphorylation-state ratio, and a greater state of reduction of the respiratory chain cytochromes b, c, and oxidase. Incubation of mitochondria in the hypotonic media caused a rapid decrease in the intermembrane and intracrystal spaces and concurrent expansion of the matrix, without changing the volume of the mitochondria. These observations indicate that expansion of the inner-membrane-matrix compartment of mitochondria in vitro specifically activates fatty acid oxidation at the site of beta-oxidation or at the site of its interaction with the respiratory chain, with a consequent increase in the states of reduction and phosphorylation of the mitochondria. Evidence is also presented which suggests that the activation of mitochondrial fatty acid oxidation by Ca2+ is initiated by a Ca2+-induced alteration of the structure or volume of the inner-membrane-matrix region.

Reduction of exogenous FMN by isolated rat liver mitochondria. Significance to the mobilization of iron from ferritin

When FMN is added to rat liver mitochondria or mitoplasts it is reduced at a rate of approx. 0.2 nmol . min-1 . mg-1 protein. Sonicated mitochondria do not reduce exogenous FMN. The reduction depends on drainage of reducing equivalents from the respiratory chain at the level of ubiquinone. The net production of reduced FMN is detectable only at oxygen concentrations less than 4-5 muM. The mitochondrial ubiquinol-FMN oxidoreductase provides a mechanism for the coupling of FMN-reduction to the reductive mobilization of iron from ferritin. The results are discussed in relation to the role of ferritin as a donor of iron to the mitochondria.

Calcium in isolated mitochondria from the left ventricular wall

The content of calcium per mg mitochondrial protein has been measured by conventional biochemical methods in myocardial tissue of some mammalian species. In addition, a method is presented for (1) the analysis of mitochondrial volumes in the same tissues and (2) calculating the amount of calcium in units of 10(6) mitochondria. It appears that a highly significant correlation exists between the calcium content and the number of mitochondria, with a positive correlation coefficient of 0.92. The mean mitochondrial volume in fractions of the rabbit myocardium was found to be 1.3386 micron3. Electron microscopic studies demonstrate pure mitochondrial fractions and only moderate structural alterations. The method described may represent a useful supplement for the estimation of calcium fluxes in mitochondria and of alterations in their volume, number and structure under conditions of myocardial ischemia.