Abstract
Cancer cells responsive to treatment with cisplatin, an anti-cancer drug, undergo apoptosis. To investigate the possible role of cation channels in the cellular response to cisplatin, we examined the activity of cation channels in cisplatin-sensitive KB-3-1 (KB) epidermoid cancer cells by the whole-cell patch-clamp method. Activity of the Ca2+-activated, intermediate conductance K+ channel (IK1) was observed during hypotonic stimulation of these cells. The channel was inhibited by the blockers clotrimazole and TRAM-34. In addition, expression of a dominant negative construct suppressed its activity. In the KCP-4 cell line, a cisplatin-resistant cell line derived from KB cells, we did not observe IK1 activity, and the channel's molecular expression, observed by semi-quantitative RT-PCR and immunostaining, appeared much reduced. To determine whether IK1 has a physiological role as part of the volume regulatory machinery in KB cells, cell volume measurements were made; it was found that regulatory volume decrease during hypotonic stress was inhibited by IK1 blockers, implicating the channel in this process. Next, we examined whether the channel has a role in the cisplatin-induced apoptosis of KB cells. It was found that IK1 blockers inhibited a cell viability decrease, as well as a caspase-3/7 activity increase, caused by cisplatin treatment. Thus, the activity of IK1, functional in cisplatin-sensitive KB cells but not in cisplatin-resistant KCP-4 cells, appears to contribute to apoptotic cell death in cisplatin-treated KB cells. [J Physiol Sci. 2008;58 Suppl:S206]
