Membrane accommodation in hypo-osmotically-treated, and in giant electrofused cells.

Many animal cells can survive a sudden reduction of medium osmolality by a factor of 3 or 5 , during which both volume and area must increase rapidly. By contrast, when many cells are fused, the total area decreases. It is an interesting question how rapidlyswelling cells meet the requirement for additional membrane area, or how the fused cells deal with the superfluous membrane. We investigated these two systems by microscopy and by measurement of the electrical membrane properties of single cells (by electro-rotation [1-3]). We used SP2/0-Ag14 mouse myeloma cells, electro-fused in hypotonic medium [ 4 ] as indicated * . Microscopy revealed normal SP2 cells to be not quite spherical, with a slightly "fuzzy" appearence to their surface. In slightly hyper-osmotic medium (330 mM inositol), the departure of the cells from spherical form became more severe, and it became difficult to obtain satisfactory electro-rotation. On the other hand, hypo-osmotically treated cells were larger (Fig.11, closely spherical, the fuzziness was absent from their surface, and they could be rotated very well. Rotation measurements yield the membrane capacity CM, which is related to membrane thickness (d) and permit-tjvjty ( c ) by: h = X . c/d, where "X" is the amount by which