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Flufenamic Acid Bi-Directionally Modulates the Transient Outward K+ Current in Rat Cerebellar Granule Cells

In this report, the effect of flufenamic acid on voltage-activated transient outward K+ current (IA) in cultured rat cerebellar granule cells was investigated. At a concentration of 20 μMto1 mM, flufenamic acid reversibly inhibited IA in a dose-dependent manner. However, flufenamic acid at a concentration of 0.1 to 10 μM significantly increased the current amplitude of IA. In addition to the current amplitude of IA, a higher concentration of flufenamic acid had a significant effect on the kinetic parameters of the steady-state activation and inactivation process, suggesting that the binding affinity of flufenamic acid to IA channels may be state-dependent. Silencing the Kv4.2, Kv4.3, and Kv1.1 genes of IA channels using small interfering RNA did not change the inhibitory effect of flufenamic on IA, indicating that flufenamic acid did not act specifically on any of the subunits of the IA-channel protein. Intracellular application of flufenamic acid could significantly increase the IA amplitude but did not alter the inhibited effect induced by extracellular application of flufenamic acid, implying that flufenamic acid may exert its effect from both the inside and outside sites of the channel. Furthermore, the activation of current induced by intracellular application of flufenamic acid could mimic other cyclooxygenase inhibitors and arachidonic acid. Our data are the first that demonstrate how flufenamic acid is able to bidirectionally modulate IA channels in neurons at different concentrations and by different methods of application and that two different mechanisms may be involved.