Background and purpose: Two-pore-domain potassium (K-2P) channels mediate potassium background (or 'leak') currents, controlling excitability by stabilizing membrane potential below firing threshold and expediting repolarization. Inhibition of K-2P currents permits membrane potential depolarization and excitation. As expected for key regulators of excitability, leak channels are under tight control from a plethora of stimuli. Recently, signalling via protein tyrosine kinases (TKs) has been implicated in ion channel modulation. The objective of this study was to investigate TK regulation of K-2P channels.Experimental approach: The two-electrode voltage clamp technique was used to record K-2P currents in Xenopus oocytes. In addition, K-2P channels were studied in Chinese hamster ovary (CHO) cells using the whole-cell patch clamp technique.Key results: Here, we report inhibition of human K(2P)3.1 (TASK-1) currents by the TK antagonist, genistein, in Xenopus oocytes (I(C5)0 10.7 mu M) and in CHO cells (IC50 12.3 mu M). The underlying molecular mechanism was studied in detail. hK(2P)3.1 was not affected by genistin, an inactive analogue of genistein. Perorthovanadate, an inhibitor of tyrosine phosphatase activity, reduced the inhibitory effect of genistein. Current reduction was voltage independent and did not require channel protonation at position H98 or phosphorylation at the single TK phosphorylation site, Y323. Among functional hK(2P) family members, genistein also reduced K(2P)6.1 (TWIK-2), K(2P)9.1 (TASK-3) and K(2P)13.1 (THIK-1) currents, respectively.Conclusions and implications: Modulation of K2P channels by the TK inhibitor, genistein, represents a novel molecular mechanism to alter background K+ currents.

Background - A high intake of dietary flavonoids, which are abundant in fruits, vegetables, tea, and wine, is known to reduce cardiovascular mortality. The effects of flavonoids on cardiac electrophysiology, which theoretically may have both antiarrhythmic and proarrhythmic consequences, have not been studied systematically to date.Methods and Results - We screened a broad spectrum of flavonoids for their inhibitory activity on HERG channels by using heterologous expression in Xenopus oocytes. At a concentration of 1 mmol/L, 10 compounds caused a significant inhibition of HERG currents, whereas 11 other flavonoids had no effect. The IC50 value for HERG block by naringenin, the most potent inhibitor, was 102.3 mumol/L in Xenopus oocytes and 36.5 mumol/L in HEK cells. To demonstrate the physiological relevance of these findings, we studied the effects of pink grapefruit juice, which contains large amounts of naringenin glycosides (>1000 mumol/L), in human volunteers. In 10 persons, we observed a peak QTc prolongation of 12.5 +/- 4.2 ms 5 hours after oral ingestion of 1 L of grapefruit juice. This effect was significant (P = 0.02).Conclusions - We found a significant QTc prolongation by grapefruit juice in healthy volunteers, probably caused by block of HERG channels by flavonoids. These findings reveal new perspectives on the potential for dietary modification of cardiac electrophysiology.

Seit Mitte der 1990er Jahre sind auf dem Gebiet der kardialen molekularen Elektrophysiologie faszinierende Fortschritte erzielt worden. Heute ist ein detailliertes Verständnis vieler genetischer und pathophysiologischer Grundlagen primär elektrischer Herzerkrankungen möglich, das einer besseren Differenzierung, Risikostratifizierung und Therapie den Weg bereitet hat. Gleichzeitig zeichnet sich zunehmend ab, dass die an seltenen monogenen Krankheitsbildern gewonnenen Erkenntnisse auch zu einem besseren Verständnis der epidemiologisch häufigeren polygenetischen und multifaktoriell bedingten Rhythmusstörungen führen werden.

Objective: The cardiac inwardly rectifying potassium current I-KI and its molecular correlates Kir2.1 and Kir2.2 play an important role in cardiac repolarisation and in the pathogenesis of hereditary long-QT syndrome (LQTS-7). Protein kinases A (PKA) and C (PKC) are key enzymes in adrenergic signal transduction, inducing arrhythmias in heart disease. This study investigated the regulation of Kir2.2 (KCNJ12) by PKA. Methods: Cloned Kir2.2 channels were expressed heterologously in Xenopus oocytes and currents were measured with the double-electrode voltage-clamp technique. Results: After activation of PKA by forskolin (100 mumol/l) or Ro-20-1724 (100 mumol/l), wild type currents at - 120 mV were increased by 93.7% and 79.0%, respectively. Coapplication of the PKA inhibitor KT-5720 (2.5 mumol/l) attenuated this effect. No significant changes were apparent after mutation of the single PKA consensus site S430. In addition, removal of all four PKC consensus sites in Kir2.2 induced a phorbolester-mediated current increase which could be suppressed by PKA inhibitors H-89 (50 mumol/l) and KT-5720 (2.5 mumol/l). Conclusions: This study demonstrates antagonistic effects of PKA and PKC in the regulation of Kir2.2. Phosphorylation by PKC has been shown to cause an inhibition of Kir2.2 currents, whereas activation of PKA leads to current upregulation. (C) 2004 European Society of Cardiology. Published by Elsevier B.V. All rights reserved.