Abstract
A modified analytical and experimental method using differential scanning calorimeter (DSC) was applied to determine the cell water transport properties of human erythrocytes during the freezing process. Using DSC, samples containing human erythrocyte cell suspensions of human erythrocytes with different cytocrits were cooled to −40°C at slow cooling rates (5°C/min) after nucleation. It was shown that latent heat release from one unit mass of the cell suspension was a linear function of cytocrits (cell numbers), with a temperature-dependent slope and intercept. Based on the theoretical model, cell volumes were calculated from the slope and intercept at corresponding temperatures. Cell water transport properties (lpg,Ea) were next calculated by curve fitting of the cell volume change during the freezing process. The results revealed that, for human erythrocyte, Lpg (Tr = 273.15 K) is 0.10 ± 0.01 μm/min ⋅ atm and E a is 279.1 ± 0.7 kJ/mol at the cooling rate of 5°C/min. For comparison, both DSC and cryomicroscopic experiments were performed on Saccharomyces cerevisia cells (cooling rate 10°C/min): results of DSC experiments showed that Lpg (Tr = 293.15 K) is (6.6 ± 0.1) × 10−2 μm/min ⋅ atm and E a is 66.6 ± 0.2 kJ/mol; results of cryomicroscope experiments showed that Lpg (Tr = 293.15 K) is (6.7 ± 0.2) × 10−2 μm/min ⋅ atm and E a is 68.3 ± 0.2 kJ/mol. These data are comparable, and in agreement with cryomicroscope experiments from independent investigators. The theoretical model and the DSC experimental procedure provide a verifiable approval to the determination of cell membrane transport properties at low temperatures and under the freezing conditions.
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