title: The contribution of ionic currents to changes in refractoriness of human atrial myocytes associated with chronic atrial fibrillation.
abstract: OBJECTIVE
  To investigate changes in human atrial single cell functional electrophysiological properties associated with chronic atrial fibrillation (AF), and the contribution to these of accompanying ion current changes.
  
  
  METHODS
  The whole cell patch clamp technique was used to record action potentials, the effective refractory period (ERP) and ion currents, in the absence and presence of drugs, in enzymatically isolated myocytes from 11 patients with chronic (>6 months) AF and 39 patients in sinus rhythm.
  
  
  RESULTS
  Stimulation at high rates (up to 600 beats/min) markedly shortened late repolarisation and the ERP in cells from patients in sinus rhythm, and depolarised the maximum diastolic potential (MDP). Chronic AF was associated with a reduction in the ERP at physiological rate (from 203+/-16 to 104+/-15 ms, P<0.05), and marked attenuation in rate effects on the ERP and repolarisation. The abbreviated terminal phase of repolarisation prevented fast rate-induced depolarisation of the MDP in cells from patients with AF. The density of L-type Ca(2+) (I(CaL)) and transient outward K(+) (I(TO)) currents was significantly reduced in cells from patients with AF (by 60-65%), whilst the inward rectifier K(+) current (I(K1)) was increased, and the sustained outward current (I(KSUS)) was unaltered. Superfusion of cells from patients in sinus rhythm with nifedipine (10 micromol/l) moderately shortened repolarisation, but had no effect on the ERP (228+/-12 vs. 225+/-11 ms). 4-Aminopyridine (2 mmol/l) markedly prolonged repolarisation and the ERP (by 35%, P<0.05). However, the combination of these drugs had no effect on late repolarisation or refractoriness.
  
  
  CONCLUSIONS
  Chronic AF in humans is associated with attenuation in adaptation of the atrial single cell ERP and MDP to fast rates, which may not be explained fully by accompanying changes in I(CaL) and I(TO).
authors.affiliation: University Department of Medical Cardiology, Royal Infirmary, 10 Alexandra Parade, G31 2ER, Glasgow, UK. A.J.Workman@clinmed.gla.ac.uk
authors.forename: A J
authors.initials: AJ
authors.lastname: Workman
authors.forename: K A
authors.initials: KA
authors.lastname: Kane
authors.forename: A C
authors.initials: AC
authors.lastname: Rankin
mesh_terms: D015761:4-Aminopyridine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000368:Aged; D001281:Atrial Fibrillation / Q000503:physiopathology*; D016275:Atrial Function; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels; D016022:Case-Control Studies; D002908:Chronic Disease; D004357:Drug Synergism; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D007473:Ion Channels / Q000187:drug effects; D017136:Ion Transport / Q000187:drug effects; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008875:Middle Aged; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D007473:Ion Channels; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D015761:4-Aminopyridine; D009543:Nifedipine