Abstracts

Abstract

In our study the effects of the disaggregation of the cytoskeleton components (actin filaments and microtubules) on the morphology of V79 fibroblasts were studied. V79 cells, in exponential phase of growth, were treated first with cytochalasin B (final concentration of 2 pmol/l) and then also with colchicine (final concentration of 1pmov1). The effect of the microfilament and the microtubule disassembling agents on cell morphology were observed by the phase contrast microscope. After cytochalasin B treatment the cell shape became globular and exhibited a few long cylindrical protrusions, while after a subsequent colchicine treatment the cells released many spherical vesicles. It is assumed that the long cylindrical protrusion is a consequence of the organization of the microtubules into a long rod which imposes a force upon the membrane and increases of the difference between the outer and the inner membrane layer areas. The process continues until the shape of the maximal possible area difference is reached. It is shown that the shapes of the extreme area difference are composed of cylindrical and spherical parts. The shape involving cylinders is relevant in the case when the rods are present in the cell while the shape involving spheres is relevant in the case when the rods are decomposed by colchicine. 'Apoptosis is a regulated and in some cases programmed way of cell death. Although apoptotic signals may be different in different cell types, they end in a common apoptotic molecular pathway with activation of cytoplasmic proteases and nuclear endonucleases. Impact of obstructed disposal of membranes on apoptosis was studied in the mammary epithelium during lactation and in the photoreceptor epithelium in time of opening of the eye. In the mammary gland, accumulation of secreted membranes was achieved by 2 days of weaning, and in retina it was achieved by 7 days of treatment with reserpine or bromocryptine. Electron microscopy revealed increased frequency of epithelial cells with typical apoptotic morphology in all cases. Milk stasis produced distention of mammary alveoli, but apocrine secretion of lipid globules appeared normal in the first 2 days of weaning. Cells with dark, condensed cytoplasm and condensed, eventually fragmented nuclei were present in the epithelium. Cellular fragments were also present in the gland lumen. They were always surrounded by a membrane and sometimes contained nuclear fiagments. Noticeable elongation of photoreceptors' outer segments was induced by bromocryptine and reserpine treatment. Shedding of packages of apical membranes, a sort of apocrine secretion, was partially prevented and condensation of cytoplasm was observed in inner segments and in synaptic regions. Condensed nuclei were also present, but no nuclear fragmentation was observed. Our results indicate strong correlation between induced apoptotic cell death and increased amount of extracellular membranes. Because membranes of lipid globules contain xanthine oxidase and membranes of photoreceptor outer segments contain ...