Characterization in Dual Activation by Oxaliplatin, a Platinum-Based Chemotherapeutic Agent of Hyperpolarization-Activated Cation and Electroporation-Induced Currents

Oxaliplatin (OXAL) is regarded as a platinum-based anti-neoplastic agent. However, its perturbations on membrane ionic currents in neurons and neuroendocrine or endocrine cells are largely unclear, though peripheral neuropathy has been noted during its long-term administration. In this study, we investigated how the presence of OXAL and other related compounds can interact with two types of inward currents; namely, hyperpolarization-activated cation current (I(h)) and membrane electroporation-induced current (I(MEP)). OXAL increased the amplitude or activation rate constant of I(h) in a concentration-dependent manner with effective EC(50) or K(D) values of 3.2 or 6.4 μM, respectively, in pituitary GH(3) cells. The stimulation by this agent of I(h) could be attenuated by subsequent addition of ivabradine, protopine, or dexmedetomidine. Cell exposure to OXAL (3 μM) resulted in an approximately 11 mV rightward shift in I(h) activation along the voltage axis with minimal changes in the gating charge of the curve. The exposure to OXAL also effected an elevation in area of the voltage-dependent hysteresis elicited by long-lasting triangular ramp. Additionally, its application resulted in an increase in the amplitude of I(MEP) elicited by large hyperpolarization in GH(3) cells with an EC(50) value of 1.3 μM. However, in the continued presence of OXAL, further addition of ivabradine, protopine, or dexmedetomidine always resulted in failure to attenuate the OXAL-induced increase of I(MEP) amplitude effectively. Averaged current-voltage relation of membrane electroporation-induced current (I(MEP)) was altered in the presence of OXAL. In pituitary R1220 cells, OXAL-stimulated I(h) remained effective. In Rolf B1.T olfactory sensory neurons, this agent was also observed to increase I(MEP) in a concentration-dependent manner. In light of the findings from this study, OXAL-mediated increases of I(h) and I(MEP) may coincide and then synergistically act to increase the amplitude of inward currents, raising the membrane excitability of electrically excitable cells, if similar in vivo findings occur.