title: Differential protein kinase C isoform regulation and increased constitutive activity of acetylcholine-regulated potassium channels in atrial remodeling.
abstract: BACKGROUND
  Atrial fibrillation (AF) causes atrial-tachycardia remodeling (ATR), with enhanced constitutive acetylcholine-regulated K+ current (I(KAChC)) contributing to action potential duration shortening and AF promotion. The underlying mechanisms are unknown.
  
  
  OBJECTIVE
  To evaluate the role of protein-kinase C (PKC) isoforms in ATR-induced I(KAChC) activation.
  
  
  RESULTS
  Cells from ATR-dogs (400-bpm atrial pacing for 1 week) were compared to control dog cells. In vitro tachypaced (TP; 3 Hz) canine atrial cardiomyocytes were compared to parallel 1-Hz paced cells. I(KAChC) single-channel activity was assessed in cell-attached and cell-free (inside-out) patches. Protein expression was assessed by immunoblot. In vitro TP activated I(KAChC), mimicking effects of in vivo ATR. Discrepant effects of PKC activation and inhibition between control and ATR cells suggested isoform-selective effects and altered PKC isoform distribution. Conventional PKC isoforms (cPKC; including PKCα) inhibited, whereas novel isoforms (including PKCε) enhanced, acetylcholine-regulated K+ current (I(KACh)) in inside-out patches. TP and ATR downregulated PKCα (by 33% and 37%, respectively) and caused membrane translocation of PKCε, switching PKC predominance to the stimulatory novel isoform. TP increased [Ca2+]i at 2 hours by 30%, with return to baseline at 24 hours. Buffering [Ca2+]i during TP with the cell-permeable Ca2+ chelator BAPTA-AM (1 μmol/L) or inhibiting the Ca2+-dependent protease calpain with PD150606 (20 μmol/L) prevented PKCα downregulation and TP enhancement of I(KAChC). PKCε inhibition with a cell-permeable peptide inhibitor suppressed TP/ATR-induced I(KAChC) activation, whereas cPKC inhibition enhanced I(KAChC) activity in 1-Hz cells.
  
  
  CONCLUSIONS
  PKC isoforms differentially modulate I(KACh), with conventional Ca(2+)-dependent isoforms inhibiting and novel isoforms enhancing activity. ATR causes a rate-dependent PKC isoform switch, with Ca2+/calpain-dependent downregulation of inhibitory PKCα and membrane translocation of stimulatory PKCε, enhancing I(KAChC). These findings provide novel insights into mechanisms underlying I(KAChC) dysregulation in AF.
authors: Department of Medicine and Research Center, Montreal Heart Institute, Montreal, Quebec, Canada.
authors: Samy
authors: S
authors: Makary
authors: Niels
authors: N
authors: Voigt
authors: Ange
authors: A
authors: Maguy
authors: Reza
authors: R
authors: Wakili
authors: Kunihiro
authors: K
authors: Nishida
authors: Masahide
authors: M
authors: Harada
authors: Dobromir
authors: D
authors: Dobrev
authors: Stanley
authors: S
authors: Nattel
mesh_terms: D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D001281:Atrial Fibrillation / Q000378:metabolism* / Q000473:pathology; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D004195:Disease Models, Animal; D004285:Dogs; D015536:Down-Regulation / Q000502:physiology*; D006325:Heart Atria / Q000378:metabolism* / Q000473:pathology; D007527:Isoenzymes / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000378:metabolism / Q000473:pathology; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*; D051571:Protein Kinase C-alpha / Q000378:metabolism; D051744:Protein Kinase C-epsilon / Q000378:metabolism; D013997:Time Factors
chemical_list: D007527:Isoenzymes; D015221:Potassium Channels; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; D051744:Protein Kinase C-epsilon; D000109:Acetylcholine; D002118:Calcium