Activation of cardiac human ether-a-go-go related gene potassium currents is regulated by ?1A-adrenoceptors

Abstract

Patients with cardiac disease typically develop life-threatening ventricular arrhythmias during physical or emotional stress, suggesting a link between adrenergic stimulation and regulation of the cardiac action potential. Human ether-a-go-go related gene (hERG) potassium channels conduct the rapid component of the repolarizing delayed rectifier potassium current, I(Kr). Previous studies have revealed that hERG channel activation is modulated by activation of the beta-adrenergic system. In contrast, the influence of the alpha-adrenergic signal transduction cascade on hERG currents is less well understood. The present study examined the regulation of hERG currents by alpha(1A)-adrenoceptors. hERG channels and human alpha(1A)-adrenoceptors were heterologously coexpressed in Xenopus laevis oocytes, and currents were measured using the two-microelectrode voltage clamp technique. Stimulation of alpha(1A)-receptors by applying 20 microM phenylephrine caused hERG current reduction due to a 9.6-mV shift of the activation curve towards more positive potentials. Simultaneous application of the alpha(1)-adrenoceptor antagonist prazosin (20 microM) prevented the activation shift. Inhibition of PKC (3 microM Ro-32-0432) or PKA (2.5 microM KT 5720) abolished the alpha-adrenergic activation shift, suggesting that PKC and PKA are required within the regulatory mechanism. The effect was still present when the PKA- and PKC-dependent phosphorylation sites in hERG were deleted by mutagenesis. In summary, cardiac repolarizing hERG/I(Kr) potassium currents are modulated by alpha(1A)-adrenoceptors via PKC and PKA independently of direct channel phosphorylation. This novel regulatory pathway of alpha1-adrenergic hERG current regulation provides a link between stress and ventricular arrhythmias, in particular in patients with heart disease.

Novel Potent Human Ether-à-Go-Go-Related Gene (hERG) Potassium Channel Enhancers and Their in Vitro Antiarrhythmic Activity

“…The hERG potassium channel has been reported to be regulated by a number of intracellular molecules and pathways, including cAMP and protein kinase A (Thomas et al, 1999;Cui et al, 2000), protein kinase C (Barros et al, 1998;Thomas et al, 2004), phospholipase C (Bian et al, 2001(Bian et al, , 2004Gomez-Varela et al, 2003), and Src tyrosine kinase (Cayabyab and Schlichter, 2002). Increase of the hERG current can be induced by the substrate of phospholipase C, phosphatidylinositol 4,5-bisphosphate (Bian et al, 2001(Bian et al, , 2004, activation of Src tyrosine kinase (Cayabyab and Schlichter, 2002), and perhaps by modulations of other pathways.…”

Muscarinic Regulation of Ether-a-go-go-Related Gene K+ Currents in Interstitial Cells of Cajal

“…The unique features of muscarinic modulation of ERG K ϩ currents in ICC may be due to the fact that we recorded from native cells, whereas most if not all reported studies on muscarinic regulation in the literature have been conducted using coexpression of both G-protein-coupled receptors and HERG/ERG K ϩ channels in expression systems (e.g., Xenopus oocytes, rat GH 3 /B 6 , Chinese hamster ovary, human embryonic kidney 293, human tsA-201) (Barros et al, 1998;Kiehn et al, 1998;Cui et al, 2000;Bian et al, 2001;Schledermann et al, 2001;Thomas et al, 2003Thomas et al, , 2004Hirdes et al, 2004). Another possible explanation is that in ICC, the ERG K ϩ channel may be coexpressed with ␤-subunits (minK or MiRP1), which have been found to coexpress with HERG K ϩ channels in native tissue and have been shown to influence HERG K ϩ channel properties (McDonald et al, 1997;Abbott et al, 1999;Weerapura et al, 2002).…”

“…Barros et al (1998) and Thomas et al (2003Thomas et al ( , 2004 have reported HERG K ϩ current modulation via a PKC-dependent mechanism based on experiments using PKC activation and inhibition in Xenopus oocytes expressing HERG K ϩ channel protein. Although it was hypothesized that PKC modulated HERG K ϩ channels by phosphorylation of PKC-dependent phosphorylation sites, deletion of these sites by mutagenesis did not prevent the response to G-protein receptor agonists or PKC activators (Thomas et al, 2003(Thomas et al, , 2004. To date, the phosphorylation-independent mechanism responsible for PKC dependent modulation remains unknown.…”

“…Several groups have investigated the modulatory capability of ERG K ϩ currents on different cell types via the activation of G-protein-coupled receptors, such as muscarinic receptor, thyrotropin-releasing hormone receptor, ␣ 1A -adrenergic receptor, and ␤-adrenergic receptors (Schledermann et al, 2001;Hirdes et al, 2004;Thomas et al, 2004). Second messengers, such as PKC and PKA, cAMP, and PIP 2 , have been reported to modulate the ERG K ϩ channel through phosphorylation sites, interaction with a cyclic nucleotide binding domain, and positively charged amino acids, respectively (Barros et al, 1998;Kiehn et al, 1998;Cui et al, 2000;Bian et al, 2001;Thomas et al, 2003).…”

Effects of the PKC inhibitors chelerythrine and bisindolylmaleimide I (GF 109203X) on delayed rectifier K+ currents

“…In the ventricular myocardium of most mammalian species, including dog and human, delayed rectifier K + current is composed of two independent components, called I Kr and I Ks (Gintant 1996, Li et al 1996. Both components are known to be under the control of the cAMP/PKA pathway, while the role of PKC in regulation of I Kr and I Ks is controversial, and therefore, poorly understood in spite of the extensive investigations of the field (Tohse 1990, Xiao et al 2003, Thomas et al 2004a, Toda et al 2007, Matavel and Lopes 2009. Appropriate approach of this problem might be the application of selective PKC inhibitors, provided that these agents fail to interact directly with the ion channels mediating delayed rectifier K + currents.…”