title: Inhibition of Kv4.3 by genistein via a tyrosine phosphorylation-independent mechanism.
abstract: The effects of genistein, a protein tyrosine kinase (PTK) inhibitor, on voltage-dependent K(+) (Kv) 4.3 channel were examined using the whole cell patch-clamp techniques. Genistein inhibited Kv4.3 in a reversible, concentration-dependent manner with an IC(50) of 124.78 μM. Other PTK inhibitors (tyrphostin 23, tyrphostin 25, lavendustin A) had no effect on genistein-induced inhibition of Kv4.3. Orthovanadate, an inhibitor of protein phosphatases, did not reverse the inhibition of Kv4.3 by genistein. We also tested the effects of two inactive structural analogs: genistin and daidzein. Whereas Kv4.3 was unaffected by genistin, daidzein inhibited Kv4.3, albeit with a lower potency. Genistein did not affect the activation and inactivation kinetics of Kv4.3. Genistein-induced inhibition of Kv4.3 was voltage dependent with a steep increase over the channel opening voltage range. In the full-activation voltage range positive to +20 mV, no voltage-dependent inhibition was found. Genistein had no significant effect on steady-state activation, but shifted the voltage dependence of the steady-state inactivation of Kv4.3 in the hyperpolarizing direction in a concentration-dependent manner. The K(i) for the interaction between genistein and the inactivated state of Kv4.3, which was estimated from the concentration-dependent shift in the steady-state inactivation curve, was 1.17 μM. Under control conditions, closed-state inactivation was fitted to a single exponential function, and genistein accelerated closed-state inactivation. Genistein induced a weak use-dependent inhibition. These results suggest that genistein directly inhibits Kv4.3 by interacting with the closed-inactivated state of Kv4.3 channels. This effect is not mediated via inhibition of the PTK activity, because other types of PTK inhibitors could not prevent the inhibitory action of genistein.
authors.affiliation: Dept. of Physiology, College of Medicine, The Catholic Univ. of Korea, 505 Banpo-dong, Socho-gu, Seoul 137-701, Korea.
authors.forename: Hee Jae
authors.initials: HJ
authors.lastname: Kim
authors.forename: Hye Sook
authors.initials: HS
authors.lastname: Ahn
authors.forename: Bok Hee
authors.initials: BH
authors.lastname: Choi
authors.forename: Sang June
authors.initials: SJ
authors.lastname: Hahn
mesh_terms: D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D004305:Dose-Response Relationship, Drug; D019833:Genistein / Q000494:pharmacology*; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D007529:Isoflavones / Q000494:pharmacology; D007700:Kinetics; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D048789:Phytoestrogens / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051672:Shal Potassium Channels / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism / Q000502:physiology*
chemical_list: D007529:Isoflavones; D048789:Phytoestrogens; D026902:Potassium Channel Blockers; D047428:Protein Kinase Inhibitors; D051672:Shal Potassium Channels; D014443:Tyrosine; C004742:daidzein; D019833:Genistein