Differential Protein Kinase C Isoform Regulation and Increased Constitutive Activity of Acetylcholine-Regulated Potassium Channels in Atrial Remodeling

Abstract

Key Words: atrial tachycardia Ⅲ protein kinase C isoforms Ⅲ remodeling A trial fibrillation (AF), the most common sustained cardiac arrhythmia, leads to atrial tachycardia-induced remodeling (ATR) that promotes AF (AF begets AF). 1 Atrial cardiomyocytes from chronic AF patients or atrialtachypaced dogs exhibit an agonist-independent inward rectifier K ϩ current with properties of the muscarinic cholinoceptor-activated K ϩ current I KACh . [2][3][4][5] Inhibition of this constitutive current (I KAChC ) with the selective Kir3 channel blocker tertiapin reverses ATR-induced action potential duration abbreviation and AF promotion. 3,4 Enhanced inward rectifier currents are particularly effective in stabilizing and accelerating atrial rotors because, in addition to reducing action potential duration, they hyperpolarize atrial cardiomyocytes and remove voltagedependent I Na inactivation. 6 The molecular basis of ATR-induced I KACh activation is poorly understood. Increased receptor-independent dissociation of G␣ and G␤␥ subunits does not appear to be involved. 3 Original received July 20, 2011; revision received August 18, 2011; accepted August 25, 2011. In July 2011, the average time from submission to first decision for all original research papers submitted to Circulation Research was 13.5 days.From Studies suggest that agonist-independent I KAch activation requires ATP, 7-9 pointing to the potential involvement of PKs. Indirect evidence suggests that in AF patients, the isoform of protein kinase C (PKC) may contribute to I KAChC activation. 10 The present study aimed to investigate the molecular basis of ATR-induced I KAChC channel activation in a dog model. Methods Animal ModelA total of 100 mongrel dogs (20 -36 kg) were divided into control and ATR groups (including both preliminary studies and work presented in the article). Animal care procedures followed National Institutes of Health guidelines (publication 85-23, revised 1996) and were approved by the Animal Research Ethics Committee of the Montreal Heart Institute. The animal model was prepared as previously described in detail. 11 Briefly, the atrioventricular node was ablated by radiofrequency-application. The right ventricle was paced at 80 bpm and the right atrium was paced at 400 bpm for 7 days. Open chest study was performed as previously described. 12 On study days, dogs were anesthetized (morphine 2 mg ⅐ kg Ϫ1 subcutaneous, ␣-chloralose 120 mg ⅐ kg Ϫ1 intravenous load, 29.25 mg ⅐ kg Ϫ1 ⅐ h Ϫ1 infusion) and mechanically ventilated. Right atrial effective refractory period was measured at basic cycle lengths of 150, 200, 250, 300, and 360 ms with 10 basic stimuli (S1) and a second stimulus (S2) with 5-ms decrements (all pulses twice-threshold, 2 ms). AF (irregular atrial rhythm Ͼ400 bpm) was induced with 1-to 10-second atrial burst pacing (10 -20 Hz, 4ϫthreshold, 2-ms pulses).Mean AF duration was determined in each dog based on 10 AF inductions for AF Ͻ5 minutes and five inductions for 5 to 30 minutes of AF. AF Ͼ30 minutes was considered sustained; c...

Interleukin-1β Reduces L-type Ca2+ Current through Protein Kinase Cϵ Activation in Mouse Heart

“…The protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA, 100 nM, Sigma) was added to cell culture media 10 min before experimentation. The cell-permeable myristoylated PKC⑀ peptide inhibitor (⑀-V1-2, 10 M) with amino acid sequence EAVSLKPT (AnaSpec) was incubated along with cytokine treatment (29,30). Recordings from cells with different treatments were all obtained on the same day.…”

“…Western Blots-The protocols used to isolate the enriched cytosolic and total membrane protein fractions (particulate fraction) as well as the Western blot analysis were previously described (29,31). Briefly, cells were washed with ice-cold extraction buffer containing a mixture of protease and phosphatase inhibitors (29) before being snap frozen and stored at Ϫ80°C for subsequent use.…”

“…Primary rabbit monoclonal anti-PKC␣ (1:2000) and anti-PKC⑀ (1:2000) antibodies were purchased from Cell Signaling (29). Polyclonal rabbit anti-PKC␤ I and anti-PKC␤ II (1:1000) were purchased from Santa Cruz Biotechnology (32).…”

Cellular and Molecular Electrophysiology of Atrial Fibrillation Initiation, Maintenance, and Progression

“…104 The rate-dependent increase in constitutively active I K,ACh is also Ca 2+ -dependent and is at least partly mediated via calpain, which breaks down classical protein kinase C type α-isoforms (Figure 6). 105 Several studies have suggested a role for small-conductance Ca 2+ -activated K + (SK) currents in AF. The expression of the SK1 subunit and SK channel open probability are enhanced in dogs with atrial tachycardia remodeling, promoting repolarization shortening, 106 whereas the inhibition of SK channels prolongs atrial repolarization and reduces AF duration in several animal models.…”

Circulation Research Thematic Synopsis

“…Differential Protein Kinase C Isoform Regulation and Increased Constitutive Activity of Acetylcholine-Regulated Potassium Channels in Atrial Remodeling; Makary et al 14 …”