Strain Rate-Dependent Membrane Reservoir- Key to Chondrocyte Death by Impact

Impact/fast loading of articular cartilage causes chondrocyte deaths. Cell membranes can sustain only 3-4% strain, but are protected from direct stretch by their membrane ruffles, also known as membrane reservoir. Based on a numerical model, we suggested that excessive tensile strain rates in chondrocyte membranes in impacted cartilage may render the membrane reservoir inaccessible, thus resulting in membrane rupture and cell death. However, experimental support for this proposal is lacking. The current study was aimed at measuring the accessible membrane reservoir size for different membrane strain rates through membrane tethering techniques. Force spectroscopy was conducted on isolated bovine chondrocytes (n=87) using atomic force microscopy. A micron-sized cantilever was used to extract membrane tethers from cell surfaces at constant pulling rates. Membrane tethers could be identified as force plateaus in the resulting force-displacement curves. Six pulling rates (1-80μm/s) were tested. The normalized membrane tether surface areas, which represent the accessible membrane reservoirs, decreased exponentially with increasing pulling rates (figure). Our findings support the hypothesis that impact-induced chondrocyte deaths are due to membrane ruptures resulting from high tensile membrane strain rates.View Large Image | View Hi-Res Image | Download PowerPoint Slide