Altered transient outward current in human atrial myocytes of patients with reduced left ventricular function.
BACKGROUND
Electrophysiologic remodeling is involved in the self-perpetuation of atrial fibrillation. To define whether differences in atrial electrophysiology already are present in patients with increased susceptibility for atrial fibrillation, we compared patients in sinus rhythm with and without heart failure.


RESULTS
Atrial specimens were obtained from patients with reduced left ventricular ejection fraction (LVEF; n = 10) and normal LVEF (n = 16) who were undergoing aortocoronary bypass surgery and from donor hearts (n = 4). Enzymatically isolated atrial myocytes were investigated by whole cell, patch clamp techniques. Total outward current was significantly larger in myocytes of hearts with low LVEF than normal LVEF (19.4 +/- 1.3 vs 15.1 +/- 1.2 pA/pF at pulses to +60 mV, respectively). Analysis of inactivation time courses of different outward current components revealed that the observed current difference is due to the transient calcium-independent outward current I(to1) which is twice as large in the low LVEF group than in the normal LVEF group (9.4 +/- 0.9 vs 4.7 +/- 0.4 pA/pF at pulses to +60 mV, respectively). I(to1) recovery from inactivation was significantly more rapid in myocytes of hearts with low LVEF, and action potential plateau in these cells was significantly shorter. The results of I(to1) and action potential measurements in atrial myocytes of donor hearts were very similar to the results of patients with preserved heart function.


CONCLUSIONS
I(to1) in human atrial myocytes of patients with reduced LVEF has an increased density and altered kinetics in sinus rhythm. These differences in outward current may explain the reduced plateau phase of action potentials.
Schreieck
J
J
I. Medizinische Klinik, Klinikum rechts der Isar and Klinik für Herzkreislauferkrankungen, Deutsches Herzzentrum, Technische Universität München, Munich, Germany. Schreieck@dhm.mhn.de
Wang
Y
Y
Overbeck
M
M
Schömig
A
A
Schmitt
C
C
D015761:4-Aminopyridine / Q000494:pharmacology; D000200:Action Potentials; D000328:Adult; D000368:Aged; D016275:Atrial Function; D002303:Cardiac Output, Low / Q000503:physiopathology; D002469:Cell Separation; D002839:Chromans / Q000494:pharmacology; D004553:Electric Conductivity; D006321:Heart / Q000187:drug effects / Q000503:physiopathology; D006339:Heart Rate; D006801:Humans; D008875:Middle Aged; D009206:Myocardium / Q000473:pathology; D018408:Patch-Clamp Techniques; D013318:Stroke Volume; D013449:Sulfonamides / Q000494:pharmacology; D013997:Time Factors; D014019:Tissue Donors; D018487:Ventricular Dysfunction, Left / Q000503:physiopathology*
D002839:Chromans; D013449:Sulfonamides; C103474:6-cyano-4-(N-ethylsulfonyl-N-methylamino)-3-hydroxy-2,2-dimethylchromane; D015761:4-Aminopyridine