LAUSR

The ability of cells to regulate their shape and volume is critical for many cell functions. How endocytosis and exocytosis, as important ways of membrane trafficking, affect cellular volume regulation is still unclear. Here, we develop a theoretical framework to study the dynamics of cell volume, endocytosis and exocytosis in response to osmotic shocks and mechanical loadings. This model can not only explain observed dynamics of endocytosis/exocytosis during osmotic shocks but also predict the dynamics of endocytosis/exocytosis during cell compressions. We find that a hypotonic shock stimulates exocytosis while a hypertonic shock stimulates endocytosis. And exocytosis in turn allows cells to have a dramatic change in cell volume but a small change in membrane tension during hyposmotic swelling, protecting cells from the rupture under high tension. Additionally, we find that cell compressions with various loading speeds induce three distinct dynamic modes of endocytosis/exocytosis. Finally, we show that increasing endocytosis/exocytosis rates reduce the changes in cell volume and membrane tension under fast cell compression, whereas they enhance the changes in cell volume and membrane tension under slow cell compression. Together, our findings reveal critical roles of endocytosis and exocytosis in regulating cell volume and membrane tension.