α&lt;sub&gt;1&lt;/sub&gt;-adrenergic Receptor Attenuates β&lt;sub&gt;1&lt;/sub&gt;-adrenergic Modulation of IKr by Protein Kinase C-dependent Suppression of Adenylyl Cyclase in Ventricular Myocytes

Sen Wang

doi:10.11648/j.ijcems.20190502.11

Abstract

The rapid delayed rectifier K+ current (Ikr) is critical for repolarization of the cardiac action potential. Previous studies have shown activated α1-adrenergic receptor (AR) attenuates β1-adrenergic regulation of Ikr while the mechanisms involved are poorly understood. To evalutate how α1-adrenergic receptor affect β1-adrenergic modulation of Ikr, whole-cell patch-clamp recordings were peformed in isolated guinea-pig ventricular myocytes. Application of xamoterol, a selective β1-AR agonist, induced a negative shift in the activation curve and Ikr current reduction by 40.50±6.66% at the test pulse of +40 mV. Forskolin and 8-Br-cAMP also resulted in Ikr reduction by 38.17±1.50% and 24.65±3.37%, respectively. Phenylephrine, a selective α1-AR agonist, prevented the activation shift and Ikr current reduction induced by xamoterol and forskolin, but not by 8-Br-cAMP. The effect of xamoterol or forskolin on Ikr was also prevented by pretreatment with PDBu, a protein kinase C (PKC) activator, while the effect of cAMP on Ikr can not, which was similar to pretreatment with phenylephrine. When cells were pretreated with chelerythrine, a specific PKC inhibitor, phenylephrine failed to prevent Ikr reduction induced by xamoterol. Our data suggests that α1-adrenergic stimulation attenuates β1-adrenergic regulation of Ikr, through PKC-dependent downregulation of adenylyl cyclase/cyclic AMP pathway.

Highlights

We confirmed that activation of β1-ARs reduced Ikr tail current in native cardiac myocytes, which could be mimicked by forskolin treatment and a membrane permeable cAMP analog, suggesting β1-AR regulate Ikr through Gs/adenylyl cyclase (AC)/cAMP pathway
We have previously found that α1- or β1-AR, when stimulated separately, reduces Ikr currents in guinea pig cardiomyocytes [19]; simultaneous activation of α1-adrenergic receptor (α1-AR) and β1-AR did not generate significant inhibitory effects [26]
We showed that the effects of α1-adrenergic receptors attenuated β1-adrenergic modulation of Ikr is mediated by protein kinase C (PKC)

Summary

Introduction

Human ether-a-go-go-related gene (hERG) potassium channels are crucial for cardiac action potential repolarization, conducting rapid delayed rectifier K+ current (Ikr) [1,2,3]. Increasing evidence has shown that hERG/Ikr channels are regulated by a variety of G protein-coupled receptors (GPCRs), including adrenergic receptors. Sympathetic regulation of cardiac hERG/Ikr current involves β-AR-dependent stimulation of adenylyl cyclase (AC) via the stimulatory G protein (Gs) and cAMP dependent activation of protein kinase A (PKA). Decrease of the hERG/Ikr current in response to β-AR is mediated by β1-AR and is the principal signaling mechanism contributing to an increase in ventricular arrhythmias during stress and exercise. Karle et al found that xamoterol, a specific β1-AR agonist, could cause 58% Ikr tail current decease and the effect were drastically reduced by PKA inhibitor KT5720. Sympathetic regulation of cardiac hERG/Ikr current involves

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