Oxaliplatin is important for treating colorectal cancer. Although oxaliplatin is highly effective, it has severe side effects, of which neurotoxicity in dorsal root ganglion (DRG) neurons is one of the most common. The key mechanisms of this neurotoxicity are still controversial. However, disturbances of calcium homeostasis in DRG neurons have been suggested to mediate oxaliplatin neurotoxicity. By using whole-cell patch-clamp and current-clamp techniques, as well as immunocytochemical staining, we examined the influence of short- and long-term exposure to oxaliplatin on voltage-gated calcium channels (VGCC) and different VGCC subtypes in small DRG neurons of rats in vitro. Exposure to oxaliplatin reduced VGCC currents (ICa(V)) in a concentration-dependent manner (1-500 μM; 13.8-63.3%). Subtype-specific measurements of VGCCs showed differential effects on ICa(V). While acute treatment with oxaliplatin led to a reduction in ICa(V) for P/Q-, T-, and L-type VGCCs, ICa(V) of N-type VGCCs was not affected. Exposure of DRG neurons to oxaliplatin (10 or 100 μM) for 24 h in vitro significantly increased the ICa(V) current density, with a significant influence on L- and T-type VGCCs. Immunostaining revealed an increase of L- and T-type VGCC protein levels in DRG neurons 24 h after oxaliplatin exposure. This effect was mediated by calcium-calmodulin-protein kinase II (CaMKII). Significant alterations in action potentials (AP) and their characteristics were also observed. While the amplitude increased after oxaliplatin treatment, the rise time and time-to-peak decreased, and these effects were reversed by treatment with pimozide and nimodipine, which suggests that VGCCs are critically involved in oxaliplatin-mediated neurotoxicity.
Keywords: Chemotherapy; Ion channels; Neuropathic pain; Neurotoxicity; Polyneuropathy; Sensory neurons.