title: Human atrial action potential and Ca2+ model: sinus rhythm and chronic atrial fibrillation.
abstract: BACKGROUND
  Understanding atrial fibrillation (AF) requires integrated understanding of ionic currents and Ca2+ transport in remodeled human atrium, but appropriate models are limited.
  
  
  OBJECTIVE
  To study AF, we developed a new human atrial action potential (AP) model, derived from atrial experimental results and our human ventricular myocyte model.
  
  
  RESULTS
  Atria versus ventricles have lower I(K1), resulting in more depolarized resting membrane potential (≈7 mV). We used higher I(to,fast) density in atrium, removed I(to,slow), and included an atrial-specific I(Kur). I(NCX) and I(NaK) densities were reduced in atrial versus ventricular myocytes according to experimental results. SERCA function was altered to reproduce human atrial myocyte Ca2+ transients. To simulate chronic AF, we reduced I(CaL), I(to), I(Kur) and SERCA, and increased I(K1),I(Ks) and I(NCX). We also investigated the link between Kv1.5 channelopathy, [Ca2+]i, and AF. The sinus rhythm model showed a typical human atrial AP morphology. Consistent with experiments, the model showed shorter APs and reduced AP duration shortening at increasing pacing frequencies in AF or when I(CaL) was partially blocked, suggesting a crucial role of Ca2+ and Na+ in this effect. This also explained blunted Ca2+ transient and rate-adaptation of [Ca2+]i and [Na+]i in chronic AF. Moreover, increasing [Na+]i and altered I(NaK) and I(NCX) causes rate-dependent atrial AP shortening. Blocking I(Kur) to mimic Kv1.5 loss-of-function increased [Ca2+]i and caused early afterdepolarizations under adrenergic stress, as observed experimentally.
  
  
  CONCLUSIONS
  Our study provides a novel tool and insights into ionic bases of atrioventricular AP differences, and shows how Na+ and Ca2+ homeostases critically mediate abnormal repolarization in AF.
authors.affiliation: Department of Pharmacology, University of California, Davis, 451 Health Sciences Dr, GBSF Room 3513, Davis, CA 95616-8636, USA.
authors.forename: Eleonora
authors.initials: E
authors.lastname: Grandi
authors.forename: Sandeep V
authors.initials: SV
authors.lastname: Pandit
authors.forename: Niels
authors.initials: N
authors.lastname: Voigt
authors.forename: Antony J
authors.initials: AJ
authors.lastname: Workman
authors.forename: Dobromir
authors.initials: D
authors.lastname: Dobrev
authors.forename: José
authors.initials: J
authors.lastname: Jalife
authors.forename: Donald M
authors.initials: DM
authors.lastname: Bers
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D001281:Atrial Fibrillation / Q000378:metabolism / Q000503:physiopathology*; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000502:physiology; D002908:Chronic Disease; D006325:Heart Atria / Q000378:metabolism / Q000503:physiopathology*; D006352:Heart Ventricles / Q000378:metabolism / Q000503:physiopathology; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D051666:Kv1.5 Potassium Channel / Q000502:physiology; D008955:Models, Cardiovascular; D032383:Myocytes, Cardiac / Q000378:metabolism / Q000473:pathology; D012849:Sinoatrial Node / Q000503:physiopathology*; D012964:Sodium / Q000378:metabolism
chemical_list: D020746:Calcium Channels, L-Type; D051666:Kv1.5 Potassium Channel; D012964:Sodium; D002118:Calcium