Mechanism Of Kv1.3 And HERG Channel Blockade By Ketanserin

Objective: In order to uncover the mechanism of the effects and the therapeutic implications of Ketanserin (KT), an antihypertensive agent, we have investigated the pharmacological effect of Ketanserin on Kv1.3 potassium channel expressed in xenopus oocytes and the biophysical properties and molecular determinants of wild type and mutant human ether-a-go-go-related gene (HERG) channel expressed in xenopus oocytes blockade by ketanserin.Method: Kv1.3 gene and HERG were subcloned into pSP64 vector. The cRNAs were prepared with SP6 RNA Polymerase after linearization of the plasmid with EcoRI. Oocytes were injected with Kv1.3 or wild type or mutant HERG cRNA and then cultured in ND-96 solution. Currents were recorded using standard two-microelectrode voltage clamp techniques in control condition or KT intervention.Result: (1) KT produced a concentration-dependent and reversible inhibition effect on Kv1.3 channel currents and the IC50 is 14.3±1.4μmol/L. KT reduced the current of Kv1.3 by43.1±3.2% at 10μmol/L, 54.1±3.2% at 20μmol/L. The main effect of KT was to decrease the current amplitude. And KT didn't have significant effect on neither activation curves nor inactivation curves. For the steady-state activation, V1/2 and k were -23.8±0.4 mV and 7.2±0.3 for control, -22.6±0.5 mV and 8.0±0.4 in the presence of 10μmol/L KT, and -22.3±0.5 mV and 8.1±0.5 in the presence of 20μmol/L KT, respectively. The V1/2 and k for the inactivation were -46.7±0.7 and 9.0±0.6 mV for the control condition and -48.4±0.7 and 8.9±0.7 mV for the effects of 10μmol/L KT, -49.2±0.6 and 8.8±0.5 of 20μmol/L KT. This differences were not statistically significant. (2) Ketanserin exhibits partially reversible channel block, that its actions are concentration dependent. It inhibited hERG currents with an IC50 of 0.02±0.01μmol/L. No significant shift in the half-maximal activation voltage was observed and it showed no voltage dependent. Under the envolope of tail protocol its inhibitory effects are significant time dependent. KT results in a significant shift in the hERG inactivation curve and could apparently accelerate the time course of inactivation and decelerate the time course of deactivation. KT binds to the open or inactivation state of the channel and that drug binding occurs at the aromatic residue Tyr652 and Phe656 in the inner cavity of the channel.Conclusion: (1) KT significantly inhibits Kv1.3 channels within the range of concentrations observed clinically. The Kv1.3 channel has been demonstrated to play an important role in human T cell activation and proliferation, therefore, we can suspect that KT could have obvious immunologic therapeutic implications as an immunomodulator in the therapy of cardiovascular diseases through the inhibitory effect of Kv1.3 channel for the regulation of T-cell activation. (2) KT exhibits an open or inactivation state-dependence of HERG channel block and Tyr-652 and Phe-656 in the putative pore cavity region are shown to play an important role in the binding.