Sreenivasan, V. K. A. | Search bioRxiv

bioRxiv2018

Electromechanics and Volume Dynamics in Non-excitable Tissue Cells

Cell volume regulation is fundamentally important in phenomena such as cell growth, proliferation, tissue homeostasis and embryogenesis. How the cell size is set, maintained, and changed over a cells lifetime is not well understood. In this work we focus on how the volume of non-excitable tissue cells is coupled to the cell membrane electrical potential and the concentration of membrane-permeable ions in the cell environment. Specifically, we demonstrate that a sudden cell depolarization using the whole cell patch clamp results in a 30 percent increase in cell volume, while hyperpolarization results in a slight volume decrease. We find that cell volume can be partially controlled by changing the chloride or the sodium/potassium concentrations in the extracellular environment while maintaining a constant external osmotic pressure. Depletion of external chloride leads to a volume decrease in suspended HN31 cells. Introducing cells to a high potassium solution causes volume increase by up to 50%. Cell volume is also influenced by cortical tension: actin depolymerization leads to cell volume increase. We present an electrophysiology model of water dynamics driven by changes in membrane potential and in the concentration of permeable ions in the cell surrounding. The model quantitatively predicts that the cell volume is determined by the total amount of intracellular ion and protein content.

biophysics↗

bioRxiv2017

Catch-slip behavior observed upon rupturing membrane-cytoskeleton bonds

Cells are capable of cytoskeleton remodeling in response to environmental cues at the plasma membrane. The propensity to remodel in response to a mechanical stimulus is reflected in part by the lifetime of the membrane-cytoskeleton bonds upon application of a tensile loading rate. We measure the lifetime and force to rupture membrane-cytoskeleton linkages of a head and neck squamous cell carcinoma (HNSCC) cell line, HN-31 by applying a tensile loading rate (< 60 pN/s) with a handle bound to a cell, while monitoring the displacement of the handle at 2 kHz after averaging. We observe the lifetime increases with loading rate, rf to a maximum after which it decreases with further increase in rf. This biphasic relationship appears insensitive to drugs that target microtubule assembly, but is no longer detectable, i.e., lifetime is independent of rf in cells with reduced active Rho-GTPases. The loading rate-time relationship resembles catch-slip behavior reported upon applying tensile loads to separate protein complexes. Under small loads the bonds catch to increase lifetimes, under larger loads their lifetime shortens and they dissociate in a slip-like manner. Our data conforms to a model that considers the membrane-cytoskeleton bonds exhibit a load-dependent conformational change and dissociate via two pathways. We also find the membrane-cytoskeleton linkages strengthen with stationary compressive load, FSC (|FSC| < 40 pN), and conclude this metastatic cell line responds to small mechanical stimuli by promoting cytoskeleton remodeling as evident by observing F-actin within the membrane nanotube (10 {micro}m length) formed after bond rupture.

biophysics↗