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 (I(A)) in cultured rat cerebellar granule cells was investigated. At a concentration of 20 microM to 1 mM, flufenamic acid reversibly inhibited I(A) in a dose-dependent manner. However, flufenamic acid at a concentration of 0.1 to 10 microM significantly increased the current amplitude of I(A). In addition to the current amplitude of I(A), 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 I(A) channels may be state-dependent. Silencing the K(v)4.2, K(v)4.3, and K(v)1.1 genes of I(A) channels using small interfering RNA did not change the inhibitory effect of flufenamic on I(A), indicating that flufenamic acid did not act specifically on any of the subunits of the I(A)-channel protein. Intracellular application of flufenamic acid could significantly increase the I(A) 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 I(A) channels in neurons at different concentrations and by different methods of application and that two different mechanisms may be involved.
Zhao
Zheng-Ge
ZG
School of Life Sciences, Institute of Brain Science, Fudan University, Shanghai 200433, P.R. China.
Zhang
Man
M
Zeng
Xi-Min
XM
Fei
Xiao-Wei
XW
Liu
Lin-Yun
LY
Zhang
Zhi-Hong
ZH
Mei
Yan-Ai
YA
D015117:5,8,11,14-Eicosatetraynoic Acid / Q000494:pharmacology; D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology; D016718:Arachidonic Acid / Q000502:physiology; D001483:Base Sequence; D002531:Cerebellum / Q000187:drug effects* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005439:Flufenamic Acid / Q000494:pharmacology*; D051662:Kv1.1 Potassium Channel / Q000502:physiology; D008969:Molecular Sequence Data; D015221:Potassium Channels / Q000187:drug effects* / Q000502:physiology; D034741:RNA, Small Interfering / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D051672:Shal Potassium Channels / Q000502:physiology
D000894:Anti-Inflammatory Agents, Non-Steroidal; D015221:Potassium Channels; D034741:RNA, Small Interfering; D051672:Shal Potassium Channels; D015117:5,8,11,14-Eicosatetraynoic Acid; D051662:Kv1.1 Potassium Channel; D016718:Arachidonic Acid; D005439:Flufenamic Acid