Nanoscale Viscosity of Cytoplasm Is Conserved in Human Cell Lines

Abstract

Metabolic reactions in living cells are limited by diffusion of reagents in cytoplasm. Any attempt to quantify the kinetics of biochemical reactions in cytosol should be preceded with careful measurements of the physical properties of the cellular interior. Cytoplasm is a complex, crowded fluid characterized by effective viscosity dependent on its structure at a nanoscopic length scale. In this work, we present and validate the model describing the cytoplasmic nanoviscosity, based on measurements in seven human cell lines, for nano-probes ranging in diameters from 1nm to 150nm. Irrespective of cell line origin (epithelial-mesenchymal, cancerous-non-cancerous, male-female, young-adult), we obtained similar dependence of the viscosity on size of nanoprobes, with characteristic length-scales of 20±11nm (hydrodynamic radii of major crowders in the cytoplasm) and 4.6±0.7nm (radii of inter-crowder gaps). Moreover, we revealed that cytoplasm behaves as a liquid for length scale smaller than 100nm and as a physical gel for larger length scales.