Chondrocytes from articular cartilage have been shown to express a wide range of ion channels and transporters. These proteins control a number of cellular functions, including maintenance of membrane potential and regulation of cell volume. Various transcript studies have identified changes in ion channel gene expression with osteoarthritis (OA). In vitro studies have shown that pro-inflammatory cytokines can induce significant chondrocyte apoptosis, one of the hallmarks of OA (Lopez-Armada et al., 2006). Increasing evidence suggests that pro-inflammatory cytokines can also directly modulate ion channel activity (Viviani et al., 2007). Here, we investigate the electrophysiological characteristics of both healthy chondrocytes and those from an in vitro inflammatory model of osteoarthritis, using patch clamp techniques and dielectrophoresis. Chondrocytes were isolated from canine articular cartilage by standard methods (Lewis et al., 2011), from dogs euthanased for unrelated clinical reasons. The in vitro model consisted of treatment with 10ng/ml TNFα and IL-1β for 72h in culture. Cells were used up to and including the third passage. Whole cell patch clamp electrophysiology was used to determine the membrane potential of the cells. 3-dimensional dielectrophoresis (DEP) technology was used to determine the DEP spectrum of the cells, the electrical properties of the plasma membrane and the cytoplasm including membrane conductance and capacitance, as well as cytoplasmic conductivity. Data are expressed as mean ± standard error, p-values are from unpaired t-tests. Healthy chondrocytes exhibit depolarised resting membrane potentials (~-10mV) so we investigated if membrane potential was affected in cells from the in vitro model, using a whole cell tail currents voltage protocol. Compared to the healthy cells, cells from the in vitro model had a whole cell reversal potential (Vrev) 16±2mV more positive (n=5, p<0.05). Healthy cells also possessed a greater whole cell conductance than cells from the in vitro model (1.8±0.6nS vs 0.9±0.1nS; p<0.05). Healthy chondrocytes had a significantly smaller capacitance than the cytokine-treated cells (4.1±0.2pF in healthy cells vs 8.7±0.5 pF/m2 in cytokine treated cells; n=35 vs 32, p<0.001) as determined by DEP. These results show significant changes in membrane properties between control cells and cells stimulated with pro-inflammatory cytokines. Future studies are necessary to determine which ion channels are contributing to these altered membrane potentials and if these changes ultimately result in altered cell function.