title: Abnormal calcium handling in atrial fibrillation is linked to up-regulation of adenosine A2A receptors.
abstract: OBJECTIVE
  Atrial fibrillation (AF) is associated with abnormal sarcoplasmic reticulum (SR) calcium release, which is promoted by adenosine A(2A) receptor (A(2A)R) activation. Here, we tested the hypothesis that abnormal calcium release in AF is linked to A(2A)R remodelling.
  
  
  RESULTS
  Western blotting and quantitative real-time PCR were used to determine A(2A)R mRNA and protein levels in right atrial samples from patients with and without AF. Effects of A(2A)R activation on calcium handling were assessed with patch-clamp technique and confocal calcium imaging. A(2A)R mRNA levels and functional A(2A)Rs were moderately up-regulated in patients with atrial dilation and markedly up-regulated in those with AF. Accordingly, A(2A)R stimulation significantly increased ryanodine receptor phosphorylation in AF patients, and spontaneous calcium waves increased moderately in myocytes from patients with atrial dilation and strongly in patients with AF (2.2 ± 2.1 to 14.3 ± 8.8 min(-1), n = 6, P = 0.01). Moreover, the high baseline level of calcium waves in AF was reduced by A(2A)R antagonists (3.5 ± 2.0 to 1.3 ± 1.3 min(-1), n = 6, P = 0.007) or adenosine deaminase (1.7 ± 1.5 to 0.5 ± 0.6 min(-1), n = 10, P = 0.02) suggesting that A(2A)Rs are activated by endogenous adenosine. Indeed, intracellular perfusion with adenosine significantly increased the calcium wave frequency (1.1 ± 0.8 to 8.2 ± 3.3 min(-1), n = 8), whereas adenosine removal from the cytosol decreased it (2.1 ± 0.9 to 0.3 ± 0.3 min(-1), n = 8, P = 0.04).
  
  
  CONCLUSIONS
  Atrial fibrillation patients show increased A(2A)R expression that may account for the high baseline level of spontaneous SR calcium release seen in myocytes from these patients, and the ability of A(2A)R antagonists to reduce this abnormal calcium release points to the A(2A)R as a novel molecular target in AF.
authors.affiliation: Cell Physiology Laboratory, Centro de Investigación Cardiovascular CSIC-ICCC Hospital de Sant Pau, Barcelona, Spain.
authors.forename: Anna
authors.initials: A
authors.lastname: Llach
authors.forename: Cristina E
authors.initials: CE
authors.lastname: Molina
authors.forename: Cristina
authors.initials: C
authors.lastname: Prat-Vidal
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Fernandes
authors.forename: Vicent
authors.initials: V
authors.lastname: Casadó
authors.forename: Francisco
authors.initials: F
authors.lastname: Ciruela
authors.forename: Carme
authors.initials: C
authors.lastname: Lluís
authors.forename: Rafael
authors.initials: R
authors.lastname: Franco
authors.forename: Juan
authors.initials: J
authors.lastname: Cinca
authors.forename: Leif
authors.initials: L
authors.lastname: Hove-Madsen
mesh_terms: D058917:Adenosine A2 Receptor Antagonists / Q000494:pharmacology; D000368:Aged; D001281:Atrial Fibrillation / Q000378:metabolism*; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D032383:Myocytes, Cardiac / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D043705:Receptor, Adenosine A2A / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D014227:Triazines / Q000494:pharmacology; D014230:Triazoles / Q000494:pharmacology; D015854:Up-Regulation
chemical_list: D058917:Adenosine A2 Receptor Antagonists; D020746:Calcium Channels, L-Type; D012333:RNA, Messenger; D043705:Receptor, Adenosine A2A; D014227:Triazines; D014230:Triazoles; C097270:ZM 241385; D002118:Calcium