Asynchronous activation of calcium and potassium currents by isoproterenol in canine ventricular myocytes

Abstract

Adrenergic activation of L-type Ca(2+) and various K(+) currents is a crucial mechanism of cardiac adaptation; however, it may carry a substantial proarrhythmic risk as well. The aim of the present work was to study the timing of activation of Ca(2+) and K(+) currents in isolated canine ventricular cells in response to exposure to isoproterenol (ISO). Whole cell configuration of the patch-clamp technique in either conventional voltage clamp or action potential voltage clamp modes were used to monitor I(Ca), I(Ks), and I(Kr), while action potentials were recorded using sharp microelectrodes. ISO (10 nM) elevated the plateau potential and shortened action potential duration (APD) in subepicardial and mid-myocardial cells, which effects were associated with multifold enhancement of I(Ca) and I(Ks) and moderate stimulation of I(Kr). The ISO-induced plateau shift and I(Ca) increase developed faster than the shortening of APD and stimulation of I(Ks) and I(Kr). Blockade of β1-adrenoceptors (using 300 nM CGP-20712A) converted the ISO-induced shortening of APD to lengthening, decreased its latency, and reduced the plateau shift. In contrast, blockade of β2-adrenoceptors (by 50 nM ICI 118,551) augmented the APD-shortening effect and increased the latency of plateau shift without altering its magnitude. All effects of ISO were prevented by simultaneous blockade of both receptor types. Inhibition of phosphodiesterases decreased the differences observed in the turn on of the ISO-induced plateau shift and APD shortening. ISO-induced activation of I(Ca) is turned on faster than the stimulation of I(Ks) and I(Kr) in canine ventricular cells due to the involvement of different adrenergic pathways and compartmentalization.

IK1-enhanced human-induced pluripotent stem cell-derived cardiomyocytes: an improved cardiomyocyte model to investigate inherited arrhythmia syndromes

“…The increased I K1 density in the I K1 -enhanced iPS-CMs was similar in magnitude to that reported in human ventricular myocytes (12). In accordance with most mammalian animal models, including human ventricular myocytes, APD shortens as pacing frequency increases (14,24) and the APD values we measured are similar to the previously reported range for human ventricular myocytes (15,16,22). Establishing a more negative resting membrane potential increases the availability of sodium and L-type calcium channels, and the dV/dt values we obtained were in the range of adult cardiomyocytes.…”

Time Course of Low-Frequency Oscillatory Behavior in Human Ventricular Repolarization Following Enhanced Sympathetic Activity and Relation to Arrhythmogenesis

“…Both in the experiments and the simulations of this study, the time required for APD to reach steadystate following sudden β-AS was found to highly vary from cell to cell. Simulated time lapses were comprised within the experimental limits quantified for the ventricular myocytes of this and other studies (Liu et al, 2012;Ruzsnavszky et al, 2014), thus confirming validation of our population of models to reproduce available evidences on the APD time course in response to β-AS.…”

“…Ventricular myocytes were isolated from the left ventricular wall of adult beagle dogs as described in Ruzsnavszky et al (2014). The isolation procedure followed a protocol approved by the local ethical committee according to the principles outlined in the 1964 Declaration of Helsinki and its later amendments.…”

“…Transmembrane potentials were measured at 37 • C by using 3 M KCl-filled sharp glass microelectrodes with tip resistance 20-40 M (Ruzsnavszky et al, 2014). The electrodes were connected to the input of an Axoclamp-2B amplifier (Molecular Devices, Sunnyvale, CA, USA).…”

“…The individual and combined roles of β-AS and mechanical stretch in determining the time lapse for LF oscillations to become visibly manifested are yet to be explored. Experimental investigations in canine ventricular myocytes have shown that APD presents slow timedependent changes following application of a constant dose of the β-adrenergic agonist isoproterenol (ISO) (Ruzsnavszky et al, 2014). The slow activation of I K currents (in particular, slow I Ks and rapid I Kr delayed rectifier currents), as compared to the very fast activation of the I Ca current, has been demonstrated to be behind such APD lag following sudden ISO exposure.…”