Xpression Of KV1.2- And KV4.2-encoding Potassium Channels In Oocytes Of Xenopus Laevis And The Modulation Of IK(KV1.2) By Bis(7)-tacrine

Bis(7)-tacrine, a novel dimeric AChE inhibitor for treatment of AD, not only inhibited AChE , but also modulate some ligand-gated ion channels such as GABAA-,nACh-,5-HT3-, NMDA-receptors. Dysfunctions of voltage-gated potassium channels play an important role in the mechanism underlying AD. The present experiments were conducted on Xenopus oocytes expressed K_V4.2 and K_V1.2 potassium channels using two-electrode voltage clamp technique to investigate the modulatory effect of bis(7)-tacrine, a novel AChE inhibitor, on IK(K_V1.2).The results obtained from our work identified that:①after microinjection of K_V4.2 mRNA, the defollicular oocytes were incubated for 48 hours, and then the transient outward currents were recorded according to a step depolarizing protocol, while in oocytes injected with K_V1.2 mRNA the slow and sustained outward currents were recorded. However, no any current was observed in control oocytes injected nothing or with dd H2O only.②bis(7)-tacrine and tacrine inhibited K_V1.2 encoding K channels expressed in oocytes of Xenopus laevis in a manner of concentration- dependence.③bis(7)-tacrine was more potent than tacrine about two order of magnitude in inhibiting IK(K_V1.2). Bis(7)-tacrine and tacrine inhibited IK(K_V1.2) with IC50 values of 0.241±0.06μM and 102.1±21.5μM respectively.④the effects of bis(7)-tacrine and tacrine on I-V curve for IK(K_V1.2) demonstrated that bis(7)-tacrine and tacrine suppressed IK(K_V1.2) at all holding potentials, while the conductance was unchanged.⑤effects of bis(7)-tacrine and tacrine on steady-state activation of IK(K_V1.2) showed that the steady-state activation curve for IK(K_V1.2) was shifted by bis(7)-tacrine and tacrine to the left, and the half maximal activation voltage decreased from -6.607±1.22mV of the control to -16.3734±1.12mV and -11.1±0.965mV in the presence of bis(7)-tacrine and tacrine, respectively.It has been identified in the present study that bis(7)-tacrine and tacrine inhibited IK(K_V1.2) markedly, while bis(7)-tacrine was more potent than tacrine. The inhibition of bis(7)-tacrine on IK(K_V1.2) was deduced to be caused by shift of steady-state activation curve for IK(K_V1.2) to the hyperpolarizing direction.