Biomedical subjects

B Hrebenda

Publications and source records attributed to B Hrebenda.

5 recordsLinked to original sources

PubMed1991

Division of Physarum mitochondria during starvation.

Microplasmodia of Physarum polycephalum used in this study form spherules after 18 h of starvation. Stereological morphometry revealed that between the 2nd and the 5th hour of starvation the number of mitochondria in 1 mm3 of cytoplasm rises from about 12 to 24 millions and the mean volume of mitochondria drops from circa 4.6 to 3.0 microns3. This denotes the synchronous division of mitochondria. The daughter mitochondria show an increase in density of the matrix and a decrease in condensation of the net of tubular cristae. The mitochondrial division, decrease in activity of the respiratory chain and maximum of its cyanide resistance occur at the same time.

Cyanides↗

PubMed1985

Influence of penicillin and nalidixic acid on growth and cell division of Escherichia coli K-12.

Ultrastructure of E. coli K-12 cells and the synthesis of DNA in bacteria treated with low concentration of nalidixic acid and penicillin was investigated. In E. coli both drugs caused inhibition of cell division in period D of the life cycle although nalidixic acid inhibits division at an earlier stage of septum formation. The ability of cells to form filaments in the presence of nalidixic acid depends on their age, i.e. time at which cells are taken from synchronous culture.

Cell Division↗

PubMed1978

Ultrastructure of the frontal cap of monotactic forms of Amoeba proteus.

The frontal cap of the monotactic form of Amoeba proteus is separated from other cell components by a continuous structure defined as the "membrane-like envelope" (MLE). It originates from the membranes of cytoplasmic vesicles and vacuoles. The border zone between the cap and the cytoplasm is strongly vacuolized. Structural differences between frontal caps, depending on the degree of their development, indicate that the growing cap gradually fills up the whole tip of an advancing pseudopodium, and at the front it reduces the cortical layer in the interstice between the MLE and the outer cell membrane, up to its eventual disrupture. This is probably the efficient cause of the specific morphological and motory pattern of monotactic amoebae. These results and conclusions are supported by an ultrastructural analysis of the artificial frontal caps obtained by injecting oil droplets into polytactic cells, a procedure transforming polytactic forms into forms morphodynamically analogous to the natural monotactic amoebae.

Amoeba↗

PubMed1975

Oriented thick and thin filaments in Amoeba proteus.

Actin and myosin filaments as a foundation of contractile systems are well established from ameba to man (3). Wolpert et al. (19) isolated by differential centrifugation from Amoeba proteus a motile fraction composed of filaments which moved upon the addition of ATP. Actin filaments are found in amebas (1, 12, 13) which react with vertebrate heavy meromyosin (HMM), forming arrowhead complexes as vertebrate actin (3, 9), and are prominent within the ectoplasmic tube where some of them are attached to the plasmalemma (1, 12). Thick and thin filaments possessing the morphological characteristics of myosin and actin have been obtained from isolated ameba cytoplasm (18, 19). In addition, there are filaments exhibiting ATPase activity in amebas which react with actin (12, 16, 17). However, giant ameba (Chaos-proteus) shapes are difficult to preserve, and the excellent contributions referred to above are limited by visible distortions occurring in the amebas (rounding up, pseudopods disappearing, and cellular organelles swelling) upon fixation. Achievement of normal ameboid shape in recent glycerination work (15) led us to attempt other electron microscope fixation techniques, resulting in a surprising preservation of A. proteus with a unique orientation of thick and thin filaments in the ectoplasmic region.

Actins↗

PubMed1975

Contractility of glycerinated Amoeba proteus and Chaos-chaos.

Immediate contact with large volumes of cold 50% (v/v) buffered glycerol preserved typical ameboid shape of Chaos chaos and Amoeba proteus with no visible distortions. These technics allowed determination of the contraction sites in these glycerinated models upon applications of ATP-Ca-Mg-solutions. The ectoplasmic tube was the main site of contraction. Preliminary EM investigations revealed thick and thin filaments, associated with the ectoplasmic tube near the plasma-lemma, which appeared to be the basis for the contractility of the ectoplasmic tube. There was no predominant contraction of the pseudopodial tips or the endoplasm in these models. The changes of volume were as much as 50%, and in some cases were not accompanied by any change in the length of the ameba; however, lengthwise contractions of the ectoplasmic tube in some amebae occurred to as much as 25%. The data substantiate a basic requirement of the ectoplasmic tube contraction theory of ameboid locomotion.

Adenosine Diphosphate↗