A comparison of cellular ultrasonic properties during apoptosis and mitosis using acoustic microscopy

Ultra-high frequency acoustic microscopy methods were used to determine the cell thickness, sound velocity, acoustic impedance, density, bulk modulus and attenuation of untreated cells during interphase and metaphase, and cells treated to induce apoptosis. Hoechst 33342, Annexin-V and propidium iodide fluorescent stains were used to identify the cell cycle stage and early/late stage apoptosis. A statistically significant increase in thickness (11.0 to 18.9 μm), decrease in bulk modulus (2.45 to 2.43 GPa) and attenuation (1.44 to 1.10dB/cm/MHz) was observed between cells in interphase and metaphase. A statistically significant increase in thickness (11.0 to 15.3 μm), sound velocity (1570 to 1588 m/s), bulk modulus (2.45 to 2.47 GPa), attenuation (1.44 to 2.00 dB/cm/MHz) and decrease in density (994 to 979 kg/m³) was observed between interphase and early apoptotic cells. A statistically significant decrease in thickness (15.3 to 12.5 μm), sound velocity (1588 to 1555 m/s), acoustic impedance (1.554 to 1.537 MRayls), bulk modulus (2.47 to 2.39 GPa), attenuation (2.00 to 1.40 dB/cm/MHz) and increase in density (979 to 988 kg/m³) was observed between early and late stage apoptotic cells. A total of 110 cells were measured, 34 interphase, 21 metaphase, 29 early apoptotic and 26 late apoptotic. The cellular properties of cells in interphase and metaphase did not significantly change, however there are significant differences between interphase and early apoptosis, and in particular early and late stage apoptosis, indicating considerable structural or organizational rearrangement is occurring.