The response of cells to freezing depends critically on the presence of an
intact cell membrane. During rapid cooling, the cell plasma membrane may no
longer be an effective barrier to ice propagation and can be breached by e
xtracellular ice resulting in the nucleation of the supercooled cytoplasm.
In tissues, the formation of intracellular ice is compounded by the presenc
e of cell-cell and cell-surface interactions. Three different hamster fibro
blast model systems were used to simulate structures found in organized tis
sues. Samples were supercooled to an experimental temperature on a cryostag
e and ice nucleated at the constant temperature. A dual fluorescent stainin
g technique was used for the quantitative assessment of the integrity of th
e cell plasma membrane. A novel technique using the fluorescent stain SYTO
was used for the detection of intracellular ice formation (IIF) in cell mon
olayers. The cumulative incidence of cells with a loss of membrane integrit
y and the cumulative incidence of IIF were determined as a function of temp
erature. Cells in suspension and individual attached cells showed no signif
icant difference in the number of cells that formed intracellular ice and t
hose that lost membrane integrity. For cells in a monolayer, with cell-cell
contact, intracellular ice formation did not result in the immediate disru
ption of the plasma membrane in the majority of cells. This introduces the
potential for minimizing damage due to IIF and for developing strategies fo
r the cryoprotection of tissues during rapid cooling. (C) 2000 Academic Pre
ss.