The cardiac work-loop technique: An in vitro model for identifying and profiling drug-induced changes in inotropy using rat papillary muscles

Abstract

The cardiac work-loop technique closely mimics the intrinsic in vivo movement and characteristics of cardiac muscle function. In this study, six known inotropes were profiled using the work-loop technique to evaluate the potential of this method to predict inotropy. Papillary muscles from male Sprague-Dawley rats were mounted onto an organ bath perfused with Krebs-Henseleit buffer. Following optimisation, work-loop contractions were performed that included an initial stabilisation period followed by vehicle control or drug administration. Six known inotropes were tested: digoxin, dobutamine, isoprenaline, flecainide, verapamil and atenolol. Muscle performance was evaluated by calculating power output during work-loop contraction. Digoxin, dobutamine and isoprenaline caused a significant increase in power output of muscles when compared to vehicle control. Flecainide, verapamil and atenolol significantly reduced power output of muscles. These changes in power output were reflected in alterations in work loop shapes. This is the first study in which changes in work-loop shape detailing for example the activation, shortening or passive re-lengthening have been linked to the mechanism of action of a compound. This study has demonstrated that the work-loop technique can provide an important novel method with which to assess detailed mechanisms of drug-induced effects on cardiac muscle contractility.

Mechanisms of flecainide induced negative inotropy: An in silico study

“…The model predictions in a myocyte within a coupled tissue environment reveal the effect of flecainide to reduce the peak of L-type calcium current. This is due to slow conduction that allows the calcium channels to begin the inactivation process during slow depolarization [ 37 ].…”

“…Most drug safety assessments associated with block of repolarization currents and consequent repolarization abnormalities. Even though more recent investigations into repolarization related safety pharmacology and its hallmark, the prolongation of the QT interval, have taken into account multi-channel block by drugs, there has not This important area of translational research is ripe for renewed investigation [6,37,10]. By assessing and revealing the fundamental ionic mechanisms associated with electrophysiological effects of flecainide and the resulting mechanical alterations, insights into promising development of new therapeutic interventions, or combinations of existing drugs used in appropriate doses may allow for minimization of unwanted side effects [47,48].…”

“…This important area of translational research is ripe for renewed investigation [ 6 , 37 , 10 ]. By assessing and revealing the fundamental ionic mechanisms associated with electrophysiological effects of flecainide and the resulting mechanical alterations, insights into promising development of new therapeutic interventions, or combinations of existing drugs used in appropriate doses may allow for minimization of unwanted side effects [ 47 , 48 ].…”

Safety pharmacology during the COVID pandemic

“…While no distinguished service award recipient was awarded in 2020, SPS provided publication awards for recognition of outstanding scientific research. The technological innovation award was given to Fletcher, Maddock, James, Wallis, and Gharanei (2020) for the publication ‘The cardiac work-loop technique: an in vitro model for identifying and profiling drug-induced changes in inotropy using rat papillary muscles’. The Translational Safety Pharmacology Award was given to Amouzadeh et al, 2019 for the publication ‘Clinical implications and translation of an off-target pharmacology profiling hit: adenosine uptake inhibition in vitro ’.…”

Investigating the role of phosphorylated regulatory light chains during heart failure progression

“…The pH was altered to 7.4 (physiologically appropriate) by gassing the buffer with 95% O2/5% CO2 for an hour. It is important for the buffer to be cold (~4°C) to slow down the metabolism of cardiomyocytes as the metabolic demands are unable to be optimally met when the blood supply to the heart is interrupted (246,247). This will minimise metabolic events such as apoptosis and preserves viable myocardium for experiments.…”