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% O₂) 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 h 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.