Concept of relative variability of cardiac action potential duration and its test under various experimental conditions.
Beat-to-beat variability of action potential duration (short-term variability, SV) is an intrinsic property of mammalian myocardium. Since the majority of agents and interventions affecting SV may modify also action potential duration (APD), we propose here the concept of relative SV (RSV), where changes in SV are normalized to changes in APD and these data are compared to the control SV-APD relationship obtained by lengthening or shortening of action potentials by inward and outward current injections. Based on this concept the influence of the several experimental conditions like stimulation frequency, temperature, pH, redox-state and osmolarity were examined on RSV in canine ventricular myocytes using sharp microelectrodes. RSV was increased by high stimulation frequency (cycle lengths <0.7 s), high temperature (above 37ºC), oxidative agents (H2O2), while it was decreased by reductive environment. RSV was not affected by changes in pH (within the range of 6.4-8.4) and osmolarity of the solution (between 250-350 mOsm). The results indicate that changes in beat-to-beat variability of APD must be evaluated exclusively in terms of RSV; furthermore, some experimental conditions, including the stimulation frequency, redox-state and temperature have to be controlled strictly when analyzing alterations in the short-term variability of APD.
Department of Physiology, Faculty of Medicine, University of Debrecen, H-4012 Debrecen, P.O.Box 22, Hungary. nanasi.peter@med.unideb.hu.
János
J
Magyar
Kornél
K
Kistamás
Krisztina
K
Váczi
Bence
B
Hegyi
Balázs
B
Horváth
Tamás
T
Bányász
Péter P
PP
Nánási
Norbert
N
Szentandrássy
D000200:Action Potentials / Q000502:physiology*; D000222:Adaptation, Physiological / Q000502:physiology*; D000818:Animals; D001683:Biological Clocks / Q000502:physiology; D002478:Cells, Cultured; D004285:Dogs; D004558:Electric Stimulation / Q000379:methods*; D006339:Heart Rate / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D032383:Myocytes, Cardiac / Q000737:chemistry* / Q000166:cytology / Q000502:physiology*; D013696:Temperature