Kathöfer Sven, Röckl Katja, Zhang Wei, Thomas Dierk, Katus Hugo, Kiehn Johann, Kreye Volker, Schoels Wolfgang, Karle Christoph
Department of Cardiology, Medical University Hospital Heidelberg, Bergheimerstrasse 58, 69115, Heidelberg, Germany.
Naunyn Schmiedebergs Arch Pharmacol. 2003 Aug;368(2):119-26. doi: 10.1007/s00210-003-0772-x. Epub 2003 Jul 19.
Modulation of the slow component of the delayed rectifier potassium current (IKs) in heart critically affects cardiac arrhythmogenesis. Its current amplitude is regulated by the sympathetic nervous system. However, the signal transduction from the beta-adrenergic system to the KvLQT1/MinK (KCNQ1/KCNE1) potassium channel, which is the molecular correlate of the IKs current in human cardiomyocytes, is not sufficiently understood. In the human heart, three subtypes of beta-adrenergic receptors (beta(1-3)-ARs) have been identified. Only beta(1)- and beta(3)-ARs have been shown so far to be involved in the regulation of IKs. Special interest has been paid to the regulation of IKs by the beta(3)-AR because of its potential importance in congestive heart failure. In heart failure beta(1)-ARs are known to be down regulated while the density of beta(3)-ARs is increased. Unfortunately, studies on the modulation of IKs by beta(3)-AR revealed conflicting results. We investigated the functional role of protein kinase C (PKC) in the signal transduction cascade between beta3-adrenergic receptors and IKs by expressing heterologously its molecular components, the KvLQT1/MinK potassium channel, together with human beta(3)-AR in Xenopus oocytes. Membrane currents were measured with the double electrode voltage-clamp technique. Using activators and inhibitors of PKC we demonstrated that PKC is involved in this regulatory process. Experiments in which the putative C-terminal PKC-phosphorylation sites in the KvLQT1 protein were destroyed by site directed mutagenesis reduced the isoproterenol-induced current to 27+/-3,5% compared to control. These results indicate that the amplitude of KvLQT1/MinK current is mainly increased by PKC activation. Our results suggest that the regulation of the KvLQT1/MinK potassium channel via beta(3)-AR is substantially mediated by PKC phosphorylation of the KvLQT1 protein at its four C-terminal PKC phosphorylation sites.
心脏中延迟整流钾电流（IKs）慢成分的调节对心律失常的发生起着关键作用。其电流幅度受交感神经系统调节。然而，从β-肾上腺素能系统到KvLQT1/MinK（KCNQ1/KCNE1）钾通道的信号转导，即人类心肌细胞中IKs电流的分子关联，目前尚未完全明确。在人类心脏中，已鉴定出三种β-肾上腺素能受体亚型（β(1 - 3)-ARs）。到目前为止，仅发现β(1)-和β(3)-ARs参与IKs的调节。由于β(3)-AR在充血性心力衰竭中的潜在重要性，人们对其对IKs的调节给予了特别关注。已知在心力衰竭中β(1)-ARs下调，而β(3)-ARs的密度增加。不幸的是，关于β(3)-AR对IKs调节的研究结果相互矛盾。我们通过在非洲爪蟾卵母细胞中异源表达其分子成分KvLQT1/MinK钾通道以及人类β(3)-AR，研究了蛋白激酶C（PKC）在β3-肾上腺素能受体与IKs之间信号转导级联反应中的功能作用。使用双电极电压钳技术测量膜电流。通过使用PKC的激活剂和抑制剂，我们证明PKC参与了这一调节过程。通过定点诱变破坏KvLQT1蛋白中假定的C末端PKC磷酸化位点的实验表明，与对照相比，异丙肾上腺素诱导的电流降低至27±3.5%。这些结果表明，PKC激活主要增加了KvLQT1/MinK电流的幅度。我们的结果表明，通过β(3)-AR对KvLQT1/MinK钾通道的调节主要是由KvLQT1蛋白在其四个C末端PKC磷酸化位点的PKC磷酸化介导的。
