Valinomycin-induced apoptosis in Chinese hamster ovary cells

Accumulating evidence endorses that excessive K+ efflux is an ionic mechanism underlying apoptosis both in neuronal and non-neuronal cells. K+ channels play important roles in mediating the pro-apoptotic K' efflux. Chinese hamster ovary (CHO) cells have been widely used for gene transfection experiments. These cells lack detectable endogenous voltage-gated K' channels. We were interested in knowing whether the absence of endogenous K' channels would render wild-type CHO cells more resistant to apoptotic death. We also wished to determine if direct stimulation of K' efflux would trigger apoptosis in these cells. Exposing CHO cells to hypoxia (1% 0,) or to a typical apoptotic insult of serum deprivation for up to 24 h did not affect cell survival. On the other hand, the K' ionophore valinomycin caused substantial cell death within 12 It of its application. Valinomycin-treated CHO cells underwent several apoptotic events, including phosphatidylserine (PS) membrane translocation, caspase-3 activation, and mitochondrial membrane depolarization during the first few hours of exposure. Reducing K' efflux by elevating extracellular K' concentrations noticeably attenuated valinomycin- induced cell death. This study reinforces a K' efflux-mediated apoptotic mechanism in CHO cells and may help to explain the unique feature of their higher tolerance to apoptosis. (c) 2006 Elsevier Ireland Ltd. All rights reserved.