Chloramphenicol-Related Changes in Mitochondrial Ultrastructure

An electron-microscopic examination of bone marrow mitochondria derived from 10 patients before and after chloramphenicol (CAP) therapy has shown that CAP induces an ultrastructural modification resulting in an increase in the density of the mitochondrial matrix. These changes resemble the condensed mitochondrial configurations which have previously been interpreted in terms of electron transfer and oxidative phosphorylation. However, in the concentrations employed in this study, CAP has no effect on mitochondrial respiration or on oxidative phosphorylation, but is a potent inhibitor of mitochondrial protein synthesis. Evidence relating this effect of the drug to its myelotoxicity has been supported by a comparative study demonstrating lack of effect of a drug such as tetracycline which is not known to be myelotoxic, and the excellent correlation between the extensiveness of mitochondrial changes in the marrow and the serum level of free CAP. The results were confirmed in a parallel study on insect flight muscle mitochondria, in which the metabolic state under which the drug is administered can be con trolled and where the regular disposition of the mitochondrial cristae provides an ideal model for the study of configurational changes.

The toxicity of streptolysin O for beating mammalian heart cells in tissue culture

Pulsating mammalian myocardial cells were found to be highly susceptible in tissue culture to rapid destruction by streptolysin O. Cessation of beating occurred almost immediately, followed within minutes by multiple cell membrane bleb formation. Parallel with these changes, the cytoplasm became intensely granular and the nuclear membrane apparently thickened when viewed by phase microscopy. At the ultrastructural level, the cell membrane blebs were found to contain relatively small numbers of granular fragments. The endoplasmic reticulum of damaged heart cells was quite swollen, and its contents were considerably condensed. The myofibers were not strikingly altered, but cytoplasmic and mitochondria vacuoles were rather abundant. Cardiac endothelial, kidney epithelial, and fibroblast cells were also susceptible to lysis by this toxin, but the reactions occurred more slowly or bleb formation was less evident. An antiserotonin drug known to be protective against streptolysin-O in vivo (UML-491), did not protect against killing of cardiac cells at the tissue culture level. Serotonin could not be detected in the culture fluid after lysis of cardiac cells by streptolysin O.

The organization And Myofilament Array of Insect Visceral Muscles

The cytological organization of three insect visceral muscles has been examined in the electron microscope. In each instance, the fibres were found to be striated, and the striation pattern has been shown to reflect the distribution along the sarcomere of two sets of myofilaments. In transverse sections of the fibre at the level of the A band, these muscles have been found to exhibit an unusual myofilament array in which each thick (myosin) filament is surrounded by twelve thin (actin) filaments rather than six, as in insect flight muscle and vertebrate skeletal muscle. The distribution of T-system tubules and cisternae of the sarcoplasmic reticulum in these visceral fibres is described, and compared with the corresponding membrane systems in other striated muscles.

Observations on the Secretory Processes in the Corpus Cardiacum of the Stick Insect, Carausius morosus

The organization of the corpora cardiaca and of the nerve tracts linking these with the brain of the stick insect has been examined in the electron microscope. Particular attention has been paid to the appearance of neurosecretory products within the axons of the nervi corporis cardiaci, and within the cell processes of the intrinsic secretory neurons of the corpus cardiacum; these observations are considered to be an essential preliminary to a consideration of the mechanism of release of secreted products from the organ into the ambient haemolymph.

The corpus cardiacum contains cells of three main categories: axons of neurons located in the brain, intrinsic secretory neurons, and glial cells. Within the organ the cellular components form a loosely knit tissue incorporating ramifying extracellular spaces confluent with the haemolymph via the peripheral basement-membrane sheath of the organ. The present electron-microscopic account relates particularly to the mode of release of neurosecretory products into the extracellular milieu. This evidence indicates that the corpus cardiacum is the site of release of both extrinsic and intrinsic secretions, but does not support the suggestion that intrinsic neurosecretory materials synthesized within the corpus cardiacum are discharged via axon terminals at sites outside the corpus cardiacum. It is suggested that release of both extrinsic and intrinsic material takes place by fusion of the membrane surrounding the neurosecretory droplet with the plasma membrane of the nerve cell in regions where the glial sheath is absent.

The evidence on the mechanism of extrusion of materials initially secreted and sequestered within nerve cells and their processes is described and discussed in terms of present concepts of the passage of neural and other materials across plasma membrane boundaries.

It is stressed that, in this functionally versatile organ, the electron microscope may reveal the mechanism of release of active neurohumoral materials, but is at present unable to differentiate between the rich variety of these pharmacologically active products which affect numerous target organs throughout the body.