Dynamic Effects of Hg2+-induced Changes in Cell Volume

Abstract

Using a microfluidic volume sensor, we studied the dynamic effects of Hg²⁺ on hypotonic stress-induced volume changes in CHO cells. A hypotonic challenge to control cells caused them to swell but did not evoke a significant regulatory volume decrease (RVD). Treatment with 100 μM HgCl₂ caused a substantial increase in the steady-state volume following osmotic stress. Continuous hypotonic challenge following a single 10-min exposure to HgCl₂ produced a biphasic volume increase with a steady-state volume 100% larger than control cells. Repeated hypotonic challenges to cells exposed once to Hg²⁺ resulted in a sequential approach to the same steady-state volume. Stimulation after reaching steady state caused a reduction in peak cell volume. Repeated stimulation was different than continuous stimulation resulting in a more rapid approach to steady state. Substituting extracellular Na⁺ with impermeant NMDG⁺ in the hypotonic solution produced a rapid RVD-like volume decrease and eliminated the Hg²⁺-induced excess swelling. The volume decrease in the presence of Hg²⁺ was inhibited by tetraethylammonium and 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid disodium, blockers of K⁺ and Cl⁻ channels, respectively, suggesting that part of the Hg²⁺ effect was increasing NaCl influx over KCl efflux. The presence of multiple phases of steady-state volume and their sensitivity to the stimulation history suggests that factors beyond solute fluxes, such as modification of mechanical stress within the cytoskeleton also plays a role in the response to hypotonic stress.