Abstract 1880: Molecular Basis of Inward-Rectifier Potassium Current Upregulation in Human Atrial Fibrillation: Contrasting Mechanisms for I
            K1
            versus Constitutive I
            KACh

Introduction: Upregulation of Kir-based inward rectifiers I K1 and constitutively active acetylcholine-regulated current (I KACh,c ) is a prominent contributor to atrial fibrillation (AF) maintenance. This study assessed occurrence and molecular basis of altered I K1 and I KACh,c in man. Methods: Left atrial samples from mitral valve repair patients (n = 21 AF; n = 20 SR) were studied. Patch-clamp was applied to record currents. Immunoblots and confocal microscopy were used to study protein content and localization. Quantitative real-time PCR was performed to study microRNA and mRNA levels. Results: I K1 and I KACh,c densities were greater in cells from AF than SR patients (at −120 mV: 3.5 ± 2.6 vs. 2.1 ± 1.1 pA/pF for I K1 and 1.3 ± 0.8 vs. 0.4 ± 0.3 pA/pF for I KACh,c ). Kir2.1 protein (underlying I K1 ) was increased by AF (Fig. ) but Kir2.3 was unchanged. Kir2.1 mRNA was increased and Kir2.3 mRNA reduced. Kir3.1 and Kir3.4 (underlying I KACh,c ) protein was unaffected. The inhibitory regulatory G-protein G αi-3 was downregulated, potentially explaining increased free G αγ and I KACh,c . No change in other regulatory proteins (RGS4, calmodulin) or subcellular channel and regulatory proteins localization occurred with AF. Kir2.1 protein expression is known to be downregulated by the microRNA miR-1: miR-1 expression was reduced by AF (Fig. ). Conclusions: Both inward rectifier currents I K1 and I KACh,c are increased in human AF. I K1 changes are caused by increased protein expression through transcriptional and post-transcriptional modifications related to miR-1 downregulation, whereas the increase in I KACh,c is functional, possibly mediated by decreased inhibitory G-protein expression.

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Molecular Basis of Downregulation of G-Protein–Coupled Inward Rectifying K+Current (IK,ACh) in Chronic Human Atrial Fibrillation

Circulation ◽

10.1161/hc4601.099466 ◽

2001 ◽

Vol 104 (21) ◽

pp. 2551-2557 ◽

Cited By ~ 175

Author(s):

D. Dobrev ◽

E. Graf ◽

E. Wettwer ◽

H.M. Himmel ◽

O. Hála ◽

...

Keyword(s):

Atrial Fibrillation ◽

G Protein ◽

Molecular Basis ◽

K Current ◽

G Protein Coupled ◽

Human Atrial Fibrillation

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Abstract 1236: A Molecular and Functional Basis for Focal Arrhythmogenesis in Heart Failure-associated Atrial Fibrillation

Circulation ◽

10.1161/circ.116.suppl_16.ii_251-b ◽

2007 ◽

Vol 116 (suppl_16) ◽

Author(s):

Yung-Hsin Yeh ◽

Reza Wakili ◽

Xiao Yan Qi ◽

Denis Chartier ◽

Stefan Kääb ◽

...

Keyword(s):

Heart Failure ◽

Atrial Fibrillation ◽

Protein Expression ◽

Action Potentials ◽

Molecular Mechanisms ◽

Potential Role ◽

Regulatory Proteins ◽

Related Protein ◽

Triggered Activity ◽

Delayed Afterdepolarizations

Introduction: Heart failure (HF) frequently causes atrial fibrillation (AF) and focal sources of unknown mechanism have been implicated. Here, we studied the potential role and molecular mechanisms of Ca 2+ handling abnormalities. Methods: Ca 2+ handling (microfluorescence, Indo-1 AM) and related protein expression (Western blot) were assessed in left atria of 20 dogs with ventricular tachypacing (240 bpm × 2 wks)-induced HF and 20 controls (CTLs). Whole-cell perforated-patch was used to record action potentials (APs), delayed afterdepolarizations (DADs) and triggered activity. Results : HF increased [Ca 2+ ] i transient amplitude from 239±24 to 444±43* nM (*P<0.05), and [Ca 2+ ] i release by 10 mM local caffeine puffs (an index of SR Ca 2+ content) from 849±71 (CTL) to 1574±169* nM (HF). Spontaneous Ca 2+ release events increased from 1.8±0.5 (CTL) to 10.7±2.1* events/run (HF). HF significantly increased APD (by ~40% at 1 Hz). DADs and triggered activity were more common in HF (15.2±2.6 triggered APs/run, vs CTL 0.4±0.2*), and were abolished by ryanodine (10 μM), but not by the I f -blocker Cs + (2 mM). HF caused profound changes in protein expression of key Ca 2+ handling and regulatory proteins (Table ). Calsequestrin, the major SR Ca 2+ -binding protein, was reduced by 32%*. Fractional RYR2 PKA (Ser2809) phosphorylation decreased by 63%*, whereas CaMKII (Ser2815) RYR2 phosphorylation increased by 221%*. The catalytic and regulatory (RII) PKA subunits were downregulated by 15%* and 73%*, whereas expression and autophosphorylation (Thr287) of CaMKIIδ were increased by 45%* and 81%* respectively. NCX1, SERCA and total, PKA and CaMKII phosphorylated SERCA-regulatory phospholamban were unchanged by HF. Conclusions: HF causes profound changes in regulation and expression of atrial Ca 2+ handling proteins, producing increased SR Ca 2+ load and release, along with DADs and triggered activity that may account for focal mechanisms that initiate and/or sustain HF-related AF.

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