USE OF A MICROCENTRIFUGE FOR PREPARATION OF ISOLATED MITOCHONDRIA AND CELL SUSPENSIONS FOR ELECTRON MICROSCOPY

METMYOGLOBIN OXIDATION DURING ELECTRON TRANSPORT REACTIONS IN MITOCHONDRIA

Studies of the intracellular role of myoglobin were carried out by recording spectrophotometric changes in acid metmyoglobin and oxymyoglobin during electron transport reactions with mitochondria prepared from pigeon heart muscle by the method of Chance and Hagihara. The absorption peak of metmyoglobin at 409 mmicro disappeared when substrate was added to normal or antimycin-inhibited preparations, and was replaced by a new maximum at 423 to 424 mmicro, identified as due to the oxidation to ferrylmyoglobin. Further investigation revealed that the oxidation of metmyoglobin took place with the simultaneous oxidation of reduced flavoprotein. Hydrogen peroxide, formed by the reaction of reduced flavoprotein with oxygen, was considered to be the probable intermediate for the oxidation of metmyoglobin in experiments in which catalase was added as a competitor for the oxidant. When DPNH was added to the reaction mixture, the reductant acted to resynthesize the ferri-derivative by reaction with ferrylmyoglobin. Oxymyoglobin could not be used in place of metmyoglobin in these systems. Under the experimental conditions, oxymyoglobin dissociated when dissolved oxygen was depleted from the medium by enzyme oxidations; the resultant ferromyoglobin underwent oxidation to metmyoglobin.

The peripheral cytoplasm of adrenocortical cells: zone-specific responses to ACTH

BACKGROUND

Differences in the cytoskeletal protein actin in cells from the zona glomerulosa and zona fasciculata would be of considerable interest because there is persuasive evidence that rat corticosteroids are secreted by mechanisms that are somewhat zone-specific. We have previously shown evidence that actin may be involved in steroid secretion, possibly in connection with changes in adrenocortical microvilli. However, the cells upon which the data were based were not separated according to zone of origin.

METHODS

Immunogold electron microscopy and morphometric procedures were used to determine whether ACTH-induced changes in the peripheral cytoplasm of isolated adrenocortical cells occur in both zona fasciculata and zona glomerulosa cells.

RESULTS

Actin immunoreactivity was more concentrated in the cytoplasm adjacent to the plasma membrane (including the cytoplasm within the microvilli) than it was in the internal cytoplasm in cells from both zones (4-6 times more concentrated in zona glomerulosa cells and 3-6 times more concentrated in zona fasciculata cells). However, the mean aggregate microvillar surface length (microvillar index) of untreated zona fasciculata cells (previously reported (Loesser and Malamed, 1987)) was 23% greater than that of untreated zona glomerulosa cells. Although ACTH (at a maximal steroidogenic concentration) had no effect on the peripheral cytoplasmic actin concentration of zona glomerulosa cells, there was a 24% increase in the aggregate microvillar length. In contrast, in zona fasciculata cells, ACTH treatment was accompanied by an increase in peripheral cytoplasmic actin concentration of 58-64% and an increase in aggregate microvillar surface length of 40% (previously reported (Loesser and Malamed, 1987)), almost twice that for zona glomerulosa cells.

CONCLUSION

The results suggest that ACTH-induced hormone release from zona fasciculata cells is mediated by increases in peripheral cytoplasmic actin and aggregate microvillar length; in zona glomerulosa cells such changes are small or absent.

Transmission electron microscopy of small numbers of sorted cells

A new method that allows the transmission electron microscopic examination of as few as 1 x 10(4) cells obtained by flow cytometric sorting is described. The approach involves "sandwiching" fixed cells in an agarose case by a microcentrifugation system consisting of small-diameter cell-centrifugation tubes and subsequent processing of the cells by conventional techniques. The advantages offered by this method are discussed.

Isolated adrenocortical cells of the domestic fowl (Gallus domesticus): steroidogenic and ultrastructural properties

Isolated adrenocortical cells from White Leghorn chickens (Gallus domesticus) were compared to those from rats (Rattus norvegicus). Cells were prepared from collagenase-dispersed adrenal glands of sexually mature male animals. Corticosterone was measured by radioimmunoassay after incubation for 2 h with steroidogenic agents. Of the four ACTH analogues used, three were 6-17 times more potent with rat cells than with fowl cells (potencies were indicated by half-maximal steroidogenic concentrations). However, 9-tryptophan (O-nitrophenylsulfenyl) ACTH was 8 times more potent with fowl cells than with rat cells, thus suggesting that ACTH receptor differences exist between the two cell types. In addition, cAMP analogues were 10 times more potent with rat cells than with fowl cells suggesting that fowl corticosteroidogenesis is less dependent on cAMP than is rat corticosteroidogenesis. At equal cell concentrations, rat cells secreted 20-40 times more corticosterone than did chicken cells when they were maximally stimulated. Although rat cells converted 8 times more pregnenolone to corticosterone than did fowl cells, the half-maximal steroidogenic concentration for pregnenolone-supported corticosterone synthesis was the same for both cell types (about 5 microM). This suggests that fowl cells have lower steroidogenic enzyme content rather than lower steroidogenic enzyme activity. An unusual feature seen in the isolated fowl adrenocortical cells was an abundance of intracellular filaments.

A light and electron microscopic study of the ciliated urn of Phasolosoma agassizii (Sipunculida)

The free swimming ciliated urn found in the coelomic fluid of Phascolosoma agassizii has been studied by electron microscopy. The urn is a multicellular structure composed of three cell types: (a) ciliated cells which possibly function in capturing cell debris and foreign particles; (b) cupola cells which are capable of phagocytozing latex particles; and (c) lobe cells which are capable of phagocytozing carbon particles. The lobes are separated from the ciliated cells by a semilunar area, with mucoprotein staining characteristics, containing fibrils which appear to be the structural support for the urn. Ciliated cells and lobes are attached to the semilunar area by hemidesmosomes.

Acute effects of ACTH on dissociated adrenocortical cells: quantitative changes in mitochondria and lipid droplets

To study the role of certain organelles in steroidogenesis, dissociated rat adrenocortical cells were incubated for two hours with ACTH at a concentration that induces a high level of steroid production. Sections of ACTH treated and untreated cells were photographed in the electron microscope, and morphometric analysis was undertaken to assess possible ACTH-induced changes in total cell volume, volume density and numerical denisty of lipid droplets and mitochondria. There was no change in total cell volume. Lipid droplet volume density and numerical density decreased. Mitochondrial volume density did not change, but numerical density increased. The decrease in lipid droplet volume density indicates a rapid depletion of cholesterol for steroid production. This depletion is almost entirely due to the disappearance of lipid droplets, rather than to an overall diminution in their size, as shown by the decrease in lipid droplet numerical density. The mitochondrial data suggest that the adrenocortical cell has an adedquate mitochondrial apparatus to respond to acute ACTH stimulation with increased steroid output without an increase inmitochondrial volume.

Separation of acinar cells from lactating mammary gland using velocity sedimentation in an isokinetic gradient of Ficoll in tissue culture medium

This report describes a procedure for the purification of acinar cells from the disaggregated lactating mammary gland of the rat. Following disaggregation of the 15 days postpartum mammary gland, two qualitatively different kinds of cells which exhibited alkaline phosphatase activity were identified. These two populations of cells were separated in a previously described isokinetic gradient of Ficoll in tissue culture medium using a centrifugal force of 55g for 14 minutes. The larger of these two types of cells was found in a well-defined subpopulation of mammary cells, 97.4 +/- 0.8% of which lacked demonstrable adenosine triphosphatase activity by light microscopy. Ultrastructurally, these cells were identified as being almost exclusively acinar cells. The potential significance of this method is discussed.

Differences in enzyme content of azurophil and specific granules of polymorphonuclear leukocytes. II. Cytochemistry and electron microscopy of bone marrow cells

In the previous paper we presented findings which indicated that enzyme heterogeneity exists among PMN leukocyte granules. From histochemical staining of bone marrow smears, we obtained evidence that azurophil and specific granules differ in their enzyme content. Moreover, a given enzyme appeared to be restricted to one of the two types. Clear results were obtained with alkaline phosphatase, but those with a number of other enzymes were suggestive rather than conclusive. Since the approach used previously was indirect, it was of interest to localize the enzymes directly in the granules. Toward this end, we carried out cytochemical procedures for five enzymes on normal rabbit bone marrow cells which had been fixed and incubated in suspension. The localization of reaction product in the granules was determined by electron microscopy. In accordance with the results obtained on smears, azurophil granules were found to contain peroxidase and three lysosomal enzymes: acid phosphatase, arylsulfatase, and 5'-nucleotidase; specific granules were found to contain alkaline phosphate. Specific granules also contained small amounts of phosphatasic activity at acid pH. Another finding was that enzyme activity could not be demonstrated in mature granules with metal salt methods (all except peroxidase); reaction product was seen only in immature granules. The findings confirm and extend those obtained previously, indicating that azurophil granules correspond to lysosomes whereas specific granules represent a different secretory product.

Oxidative phosphorylation by muscle mitochondria of dysstrophic mice

Oxidative phosphorylation was studied in mitochondria isolated from the skeletal muscle of control and dystrophic mice of the Jackson Laboratory strain 129/Re, aged 32–104 days. The isolation procedure included a preliminary incubation of the muscle minced in a medium containing a proteinase (Nagarse) followed by gentle homogenization and differential centrifugation. Polarographic estimations in the presence and absence of adenosine diphosphate (ADP) indicated that the rate of oxygen uptake, ADP/0 ratio, respiratory control ratio, and phosphorylation rate were not significantly different in the mitochondria isolated from control and dystrophic mice. Bovine serum albumin increased the ADP/0 and respiratory control ratios, but the values for the control and dystrophic preparations again did not differ significantly in the presence of albumin.

CONTROL OF REDUCED NICOTINAMIDE-ADENINE DINUCLEO-TIDE OXIDATION BY PIGEON-HEART MITOCHONDRIA

The rate of oxidation of 10–35 μM reduced nicotinamide–adenine dinucleotide (NADH) by pigeon-heart mitochondria was increased not only by osmotic swelling and sonic disruption of the organelles but also by milder procedures such as washing or dilution, which had no deleterious effect on the P: O and respiratory control ratios when glutamate was the substrate. In all cases, the enhanced oxidation of 10 μM NADH was suppressed by 5 mM adenosine triphosphate (ATP). From these and other findings it was concluded that the access of extra-mitochondrial NADH to the respiratory chain is controlled at a minimum of two sites. Control of NADH flux through the first site is lost after treatment of the mitochondria by procedures which increase their permeability. A second level of NADH control survives sonic disruption of the mitochondria and is a site at which the oxidation of 10 μM NADH is stimulated by Piand inhibited by ATP, adenosine diphosphate (ADP), and oxidized nicotinamide–adenine dinucleotide (NAD+). The ATP and ADP effects at this level are not blocked by oligomycin. Magnesium releases the adenine nucleotide inhibition of NADH oxidation under certain conditions, but its site and mode of action is not clear as yet. In these experiments, NADH oxidation was determined polarographically and photometrically at 28° in a medium containing 0.23 M mannitol, 0.07 M sucrose, 0.02 M Tris–chloride, and 0.02 mM ethylenediamine tetra-acetic acid (EDTA) at pH 7.2.

Electron microscope studies on enzyme activity and the isolation of thiohydantoin-induced myelin figures in rat liver

Characteristic cytoplasmic inclusions (myelin figures), consisting of concentric multilaminar paired membranes surrounding one or more lipid bodies, were produced in rat liver parenchymal cells by incorporating high doses of an anticonvulsant agent (Bax 422Z) into the animals' diet. Enzymatic reaction product (presumably lead phosphate) was found around the central fat of these myelin figures in liver which had been fixed in glutaraldehyde, incubated in Wachstein and Meisel's medium containing adenosine triphosphate or inosine tri- or diphosphate, postosmicated, embedded in epoxy resin, and examined in the electron microscope. In an attempt to isolate myelin figures, fresh liver from medicated rats was homogenized and differentially centrifuged. Thin sections of osmium tetroxide-fixed, Epon-embedded pellets from each fraction were examined with the electron microscope. The concentric membranous whorls, which are probably derived from cisternae of the endoplasmic reticulum, broke up as the cells were disrupted and became inextricably mixed with the microsomal fraction. However, when liver previously fixed in formalin for 24 hours was homogenized, the myelin figures remained intact.