Effect of tyrphostin AG879 on Kv 4.2 and Kv 4.3 potassium channels.
OBJECTIVE
A-type potassium channels (IA) are important proteins for modulating neuronal membrane excitability. The expression and activity of Kv 4.2 channels are critical for neurological functions and pharmacological inhibitors of Kv 4.2 channels may have therapeutic potential for Fragile X syndrome. While screening various compounds, we identified tyrphostin AG879, a tyrosine kinase inhibitor, as a Kv 4.2 inhibitor from. In the present study we characterized the effect of AG879 on cloned Kv 4.2/Kv channel-interacting protein 2 (KChIP2) channels.


METHODS
To screen the library of pharmacologically active compounds, the thallium flux assay was performed on HEK-293 cells transiently-transfected with Kv 4.2 cDNA using the Maxcyte transfection system. The effects of AG879 were further examined on CHO-K1 cells expressing Kv 4.2/KChIP2 channels using a whole-cell patch-clamp technique.


RESULTS
Tyrphostin AG879 selectively and dose-dependently inhibited Kv 4.2 and Kv 4.3 channels. In Kv 4.2/KChIP2 channels, AG879 induced prominent acceleration of the inactivation rate, use-dependent block and slowed the recovery from inactivation. AG879 induced a hyperpolarizing shift in the voltage-dependence of the steady-state inactivation of Kv 4.2 channels without apparent effect on the V1/2 of the voltage-dependent activation. The blocking effect of AG879 was enhanced as channel inactivation increased. Furthermore, AG879 significantly inhibited the A-type potassium currents in the cultured hippocampus neurons.


CONCLUSIONS
AG879 was identified as a selective and potent inhibitor the Kv 4.2 channel. AG879 inhibited Kv 4.2 channels by preferentially interacting with the open state and further accelerating their inactivation.
State Key Laboratory of Bioactive Substances and Functions of Natural Medicines, Institute of Materia Medica, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China.|The Solomon H. Snyder Department of Neuroscience, High Throughput Biology Center and Johns Hopkins Ion Channel Center, Johns Hopkins University, Baltimore, MD, USA.
Haibo
H
Yu
The Solomon H. Snyder Department of Neuroscience, High Throughput Biology Center and Johns Hopkins Ion Channel Center, Johns Hopkins University, Baltimore, MD, USA.
Beiyan
B
Zou
State Key Laboratory of Bioactive Substances and Functions of Natural Medicines, Institute of Materia Medica, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China.
Xiaoliang
X
Wang
The Solomon H. Snyder Department of Neuroscience, High Throughput Biology Center and Johns Hopkins Ion Channel Center, Johns Hopkins University, Baltimore, MD, USA.
Min
M
Li
D000818:Animals; D016466:CHO Cells; D002478:Cells, Cultured; D006224:Cricetinae; D003412:Cricetulus; D057809:HEK293 Cells; D006624:Hippocampus / Q000166:cytology; D006801:Humans; D009474:Neurons / Q000187:drug effects / Q000469:parasitology; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D017207:Rats, Sprague-Dawley; D051672:Shal Potassium Channels / Q000037:antagonists & inhibitors* / Q000502:physiology; D020032:Tyrphostins / Q000494:pharmacology*
C081020:AG-879; D026902:Potassium Channel Blockers; D051672:Shal Potassium Channels; D020032:Tyrphostins