Further evidence in support of cell-surface-associated deoxyribonucleic acid in tumor cells: an autoradiographic study.

Ascites sarcoma-180 cells, when stained with platinum-pyrimidine complexes as the sole electron dense stain, show distinct dense patches to granular appearance on the surface of the plasma membrane which has been suggested to be attributable to deoxyribonucleic acid. Swiss Webster mice, 4-5 weeks of age, weighing 24-26 g with 4 X 10(6) ascites sarcoma-180 cells when injected with 3 X 7.0 micronC of tritiated thymidine on day 5 of the tumor implant, show specific labeling on the plasma membrane surface. The photopositive silver grain distribution in both the light and electron microscope autoradiograms when followed from the nucleus outwards show a distinct peak over the nucleus and the plasma membrane. The quantity and origin and role of this surface-associated deoxyribonucleic acid is not clear.     

Cryomicroscopic determination of the membrane osmotic properties of human monocytes at subfreezing temperatures

Monocytes were isolated from fresh whole human blood and resuspended in Hanks balanced salt solution; a portion of the cells was mixed with an equal volume of 2M dimethyl sulfoxide (DMSO) to form a 1 M solution. Microliter volumes of cell suspension were placed directly onto a computer-controlled cryostage and cooled to a predetermined subzero temperature. Ice was nucleated in the extracellular medium and a continuous video record was made of the subsequent osmotically induced volume changes of individual cells owing to exposure to the concentrated extracellular solutes. Selected micrographs emphasizing the initial transient data were digitized for computer analysis with an interactive boundary tracing algorithm to determine metric parameters of specific cells, and apparent volume changes were measured as a function of elapsed time after nucleation. The Kedem-Katchalsky-coupled transport equations were fit to the data using a network thermodynamic model implemented on a microcomputer to determine values for the permeability properties Lp, omega, and sigma. Experiments were performed over the temperature range from -7 degrees to -10 degrees C. Cells pre-equilibrated with DMSO had a lower Lp and a higher activation energy, delta E, than without additive, although the statistical significance of the difference could not be substantiated. It was found that the movement of DMSO across the plasma membrane in response to extracellular freezing was apparently so much smaller than the water flux that values for omega and sigma could not be determined from the data base.