Inertial picobalance reveals fast mass fluctuations in mammalian cells

https://www.nature.com/articles/nature24288

David Martínez-Martín, Gotthold Fläschner, Benjamin Gaub, Sascha Martin, Richard Newton, Corina Beerli, Jason Mercer, Christoph Gerber & Daniel J. Müller

• Use a highly sensitive balance to measure the mass of single or multiple adherent cells in culture conditions over days with millisecond time resolution and picogram mass sensitivity 
• The mass of living mammalian cells varies by around 1-4% over timescales of seconds throughout the cell cycle
• These mass fluctuations are linked to ATP synthesis and water transport
• The balance works by oscillating a microcantilever immersed in cell media at the microcantilever's natural frequency. A cell is grown at the tip of the microcantilever. The frequency and amplitude of the vibrations of the microcantilever can be measured using a laser. These data can be used to infer the mass of the cell growing at the tip.
• Blocking aquaporins reduced the amplitude of slow mass fluctuations (period ~17s) by a factor of 4
• Inhibition of ATP synthesis in starved cells reduced the amplitude of slow mass fluctuations by a factor of ~4, and reduced the amplitude of fast mass fluctuations by around 1/3.