Biotransport and intracellular ice formation phenomena in freezing human embryonic kidney cells (HEK293T)

The objective of this study is to determine the cryobiological characteristics of human embryonic kidney (HEK293T) cells. The cell membrane hydraulic conductivity (Lpg) and the activation energy of water transport (ELp) were determined in the absence/presence of cryoprotectant agent (CPA), while the nucleation rate kinetic and thermodynamic parameters (ΩoSCN and κoSCN) were determined in the absence of CPA. Since dehydration and intracellular ice formation (IIF) are two factors that may cause damage to cells during the freezing process, systematical freezing experiments were carried out at different cooling rates (5, 10, 15, 20, 30, and 60 °C/min) under the commercial available cryomicroscopy (FDCS 196, Linkham, Waterfield, UK) to further explore the cryoinjury mechanism for HEK293T cells. By simultaneously fitting the water transport equation to the experimentally measured volumetric shrinkage data at 5, 10, and 15 °C/min, the “combined best fit” membrane permeability parameters for HEK293T cells in both phosphate buffer saline (PBS) and CPA media (0.75M Me2SO in PBS) are determined. They are Lpg = 2.85 × 10−14 m/s/Pa (0.17 μm/min/atm), ELp = 142.91 kJ/mol (34.13 kcal/mol) (R2 = 0.990), and Lpg[cpa] = 2.73 ± 0.44 × 10−14 m/s/Pa (0.16 ± 0.03 μm/min/atm), ELp[cpa] = 152.52 ± 27.69 kJ/mol (36.42 ± 6.61 kcal/mol) (R2 = 0.993), respectively. An optimal cooling rate Bopt (the highest cooling rate without IIF) was determined to be 14.24 °C/min in the absence of CPA. Additionally, the ice nucleation parameters (ΩoSCN and κoSCN) were averaged to be 1.31 ± 0.11 × 108 m−2 s−1 and 7.67 ± 2.55 × 109 K5 for the cooling rates 20, 30, and 60 °C/min.