© 2004 by European Society of Cardiology
Copyright © 2004, European Society of Cardiology
If in left human atrium: a potential contributor to atrial ectopy
aInstitut für Medizinische Physik und Biophysik, Medizinische Universität Graz, Harrachgasse 21, A-8010 Graz, Austria
bUniversitätsklinik für Chirugie, Medizinische Universität Graz, Auenbruggerplatz 5, A-8036 Graz, Austria
* Corresponding author. Tel.: +43 316 380 4137; fax: +43 316 380 7746. Email address: bernd.koidl{at}meduni-graz.at
Objective: The left human atrium plays an important role in initiation of atrial fibrillation (AF) and the hyperpolarization activated cation current (If) is a candidate for contributing to abnormal automaticity. However, electrophysiological data concerning If are not available in this cardiac region and we therefore investigated If in human left atrial tissue.
Methods: Human atrial myocytes were isolated from the left atrial appendage (LAA) and the left atrial wall (LAW) obtained from patients undergoing open heart surgery. If was measured with the whole-cell patch-clamp technique.
Results: If densities between –70 and –110 mV were found to be significantly higher in LAA than in LAW cells. Furthermore, in the group of LAA cells the half maximal activation potential (V1/2) was found to be less negative (V1/2 of –84.3±1.9 mV, n=14/9) compared to LAW cells (V1/2 of –97.8±2.1 mV, n=28/9). Beta-adrenergic receptor stimulation with isoproterenol (1 µM) caused an acceleration of current activation and a V1/2 shift to more positive potentials in cells of both regions (LAA: 8.8±2.3 mV, n=6/4 and LAW: 8.9±2.6 mV, n=6/4). Simulations using a mathematical model of the human atrial myocyte demonstrated that If was able to induce spontaneous activity in the model at a regular rhythm due to the interplay of If, Na+/Ca2+ exchange current and Ca2+ release of the sarcoplasmic reticulum (SR).
Conclusions: Our study revealed the presence of If in left atrial myocytes and showed that If parameters depend on atrial region. If current densities were sufficient to convert the mathematical model of a quiescent human atrial cell into a "pacemaker cell". These data support the hypothesis of If as a contributor to abnormal automaticity in human atrial tissue.
KEYWORDS Human left atrial myocytes; Patch clamp; Pacemaker current; Computer modeling; Atrial ectopy
Time for primary review 26 days
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