Numerous biochemical and drug transport studies have focused on the role of the plasma membrane or membrane-associated processes in anthracycline and vinca alkaloid resistance. Cationized ferritin, which binds electrostatically to anionic sites on the plasma membrane, was used as a membrane marker in a morphometrical ultrastructural study. The nonspecific adsorptive endocytosis was significantly increased in Ehrlich ascites tumor cell lines resistant to daunorubicin (DNR), doxorubicin, vincristine, and vinblastine compared to that in sensitive cells. Thus cells resistant to DNR internalized 2.04% of their plasma membrane per minute, in contrast to 1.17% in sensitive cells. Because the measured cell surface areas in sensitive and resistant cells were unchanged during the experiments, increased membrane traffic (recycling) from intracytoplasmic compartments to the plasma membrane must have occurred in resistant cells. Possible implications of these findings include a resistance-linked phenotype without significance for resistance per se, an increase in membrane repair, and a connection between increased membrane traffic and increased active drug extrusion in resistant cells.

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The sequential morphology of vascular smooth muscle cell involution and physiological cell death was studied by electron microscopy on rat incisors. Concurrently with changes in the pulp of the continuously growing incisor, its arterioles pass through a cycle of growth, remodeling, regression and decay. During the cycle, smooth muscle cells of the arterioles were observed to involute by segregation of cytoplasmic components, formation of autophagic and digestive vacuoles and shedding of cell fragments. Phagocytic vacuoles were found in neighbouring muscle cells and in adventitious macrophages. Concomitant with the involution in some cells, physiological death was observed among other smooth muscle cells. This appears as an apoptosis with sequential transformations of polyribosomes into monoribosomes, nuclear and cytoplasmic condensation, and finally fragmentation followed by phagocytosis mainly by adventitious macrophages. Knowledge of the features of physiological involution and cell death of the vascular smooth muscle cells may be of importance not only in studies of functional remodeling and adaption, but also in the interpretation of vascular lesions.

– To study cytological changes in the migrating cell layer of the ameloblasts in the rat incisor with semithin Epon sections the ideal section plane would consequently be along the midsagittal plane of the incisor. However, the small dimensions and the complex three‐dimensional structure of the apical part of the odontogenic organ covered by alveolar bone make it difficult to orientate and position sections in the midsagittal plane. Serial sectioning of the apical half of the maxillary incisor in the horizontal and sagittal planes clarified the relation of the midsagittal plane of the odontogenic organ to the alveolar bone, and the changes of the sectional profile of the odontogenic organ as a function of its position on the transverse axis of the incisor. From this information a method was designed whereby the two axes of the midagittal plane were marked directly on the block surface before sectioning, and the position of sections in the midsagittal zone of the ameloblasts standardized.

Paratesticular sarcomas are rare, especially the malignant mesenchymoma. To our knowledge only four cases of paratesticular malignant mesenchymoma have been described previously. All were localized to the spermatic cord. We present a case of malignant mesenchymoma in the scrotum free of the spermatic cord.