Expression of L-type Ca²⁺ channels (LTCC) and Na+-Ca²⁺ exchanger (NCX) 1 in AF animals and in SR controls.

<p><b>a, b</b> Regulatory LTCC α₂ subunit was significantly downregulated in AF animals, whereas the pore forming α_1c subunit was not affected. <b>c</b> AF lead to significant upregulation of the NCX1 transporter. Representative Western blots and mean (± SEM) optical density data normalized to GAPDH are displayed (n = 5 animals per group). *<i>P</i> < 0.05; ***<i>P</i> < 0.001.</p

Analysis of ryanodine receptor (RyR) and phosphorylated ryanodine receptor (p-RyR) levels in SR and AF pigs.

<p><b>a</b> Total RyR protein did not differ between animal groups. <b>b, c</b> PKA-phosphorylated RyR at Ser2808 was reduced, while CaMKII-phosphorylated RyR at Ser2814 was not affected by AF. <b>d</b> Relative p-RyR_Ser2808 but not p-RyR_Ser2814 content was diminished in atrial tissue obtained from n = 5 animals per group. Original Western blots and mean normalized optical density data are provided (*<i>P</i> < 0.05).</p

AF-induced remodeling of Ca²⁺-calmodulin-dependent protein kinase II (CaMKII) δ and protein kinase A (PKA).

<p>Representative Western blots and mean optical density values normalized to glyceraldehyde 3-phosphate dehydrogenase (GAPDH) are displayed relative to sinus rhythm (SR) controls. <b>a,</b> Absolute expression levels of the reference protein, GAPDH, were note affected by AF. <b>b, c</b> Normalized protein expression of total CaMKIIδ and phosphorylated CaMKIIδ (Thr286) in AF animals compared to SR. <b>d</b> Relative CaMKIIδ autophosphorylation at Thr286 was not different between animal groups. <b>e, f</b> Protein levels of catalytic PKA Cα/β subunits (PKA_C) and of phosphorylated regulatory RIIα subunits (PKA_RII) in AF and SR animals. Mean values obtained from five animals per group are provided ± SEM; *<i>P</i> < 0.05.</p

Remodeling of Ca²⁺ handling proteins during atrial fibrillation and heart failure.

<p>Changes in protein expression are indicated by arrows (orange color). Solid black arrows indicate transport directions of Ca²⁺ or Na⁺ ions, respectively. Decreased levels of Ca²⁺-calmodulin-dependent protein kinase (CaMK) IIδ and protein kinase A (PKA) causes hypophosphorylation of phospholamban (PLN) and ryanodine receptor (RyR) 2, leading to reduced Ca²⁺ uptake into the sarcoplasmic reticulum through sarcoplasmic reticulum Ca²⁺-ATPase (Serca) 2a. Increased intracellular Ca²⁺ levels and upregulation of Na⁺-Ca²⁺ exchanger (NCX) 1 expression enhance electrogenic Na⁺-Ca²⁺ exchange. This mechanism is attenuated by reduced L-type calcium channel (LTCC) expression that limits systolic Ca²⁺ influx.</p

Alterations of sarcoplasmic reticulum Ca²⁺-ATPase (Serca) 2a and its regulator phospholamban (PLN) during AF.

<p>Total PLN (<b>a</b>) and PLN phosphorylated by CaMKII (Thr17; <b>b</b>) or PKA (Ser16; <b>c</b>) was downregulated in AF animals. <b>d</b> Phosphorylation levels relative to total PLN. <b>e</b> Serca2a protein analysis revealed a trend towards reduced protein expression associated with AF. Mean ± SEM optical density data normalized to GAPDH obtained from n = 5 Western blots per group are displayed. *<i>P</i> < 0.05; **<i>P</i> < 0.01.</p

Clinical findings in AF pigs subjected to atrial tachypacing.

<p><b>a</b> Representative ECG recordings at baseline and after atrial fibrillation (AF) induction by atrial burst pacing show sinus rhythm on day 0 and AF on day 7. <b>b</b> Mean heart rates assessed by daily ECG measurements from AF animals (n = 5). <b>c-f</b> Atrial effective refractory periods (AERP; <b>c</b>, <b>d</b>) and corrected sinus node recovery time (SNRT; <b>e</b>, <b>f</b>) at baseline and prior to euthanization at day 7 in AF pigs (n = 5). <b>g, h</b> Echocardiographic analysis of left ventricular ejection fraction (EF) and left atrial (LA) diameter. Data are given as mean ± SEM; *<i>P</i> < 0.05; **<i>P</i> < 0.01.</p