A physical characterization of GAP A3 hybridoma cells: Morphology, geometry, and mechanical properties

Abstract

Morphological, geometrical, and rheological properties of the GAP A3 hybridoma cell line have been evaluated as a function of the cell cycle. Interference contrast video microscopy and scanning electron microscopy (SEM) showed that a sample of cells taken from the middle of the exponential growth phase displayed a range of cell morphologies, consistent with a heterogeneous growing culture. Micropipet manipulation was used to measure the geometrical (cell volume) and mechanical (cortical tension and apparent cell viscosity) properties of single cells selected at random from a sample in the middle of the exponential growth phase. Consistent with the range of morphologies, cell volumes (1400 to 5700 microm(3)) and apparent viscosities (430 to 1.2 x 10(4) P) showed a wide range of values at 37 degrees C, demonstrating that a hybridoma cell line cannot be characterized by a single value for any one property, and that properties must be related to their cycle dependence when considering proliferating cells. Direct, video-microscopic observation of synchronized cells, and of individual cells that were followed throughout their cell cycle, allowed us to correlated distinct morphologies with phases of the cell cycle. As the cell cycle progresses, an increase in cell volume by a factor of 3 to 4 is accompanied by an overall increase in apparent cell viscosity by approximately the same ratio, consistent with an accumulation of more cytoplasmic material in the older cells. Also, a decrease in average apparent viscosity by a factor of 10. These results are important in order to evaluate the possible role of certain structural, cell-cycle dependent features in shear and abrasion sensitivity. This is a problem of current concern in the bioreactor culture of mammalian cells.