Manual patch clamp

Stable action potentials can be recorded from both spontaneously beating or stimulated cardiomyocytes. Compound effects are quantified against a number of key action potential parameters, such as action potential duration (APD) which can be a surrogate marker for prolongation of the in vivo QT interval. Excessive prolongation of the APD can elicit early after depolarisations (EADs), which are considered to trigger arrhythmias such as Torsades de Pointes (TdP).

Stimulated Action Potentials

Stable action potential recordings can be taken for up to one hour using stimulation via a recording bath field potential or current injection through the recording pipette. This enables application of multiple concentrations of a compound during a single experiment (see panel below). Frequency-dependent effects on action potential parameters can also be investigated in this assay format.

CiPA toolbox compounds can help us to identify and quantify the roles of key cardiac ion channels. For example, exposure to the hERG inhibitor dofetilide results in action potential prolongation, arrhythmogenesis and early after depolarisations (EADs), demonstrating the proarrhytmic effect of a Torsadogenic compound in vitro.

Spontaneous action potential recordings

iPSC-derived cardiomyocytes possess intrinsic pacemaker activity, resulting in spontaneous action potential firing. This allows us to determine the effect of a test compound on action potential firing frequency and to identify compounds with the potential to slow (bradycardia) or increase (tachycardia) heart rate in vivo. Metrion has tested a toolbox of compounds with cardiac activity and confirmed their anticipated effect on spontaneous action potential parameters, which were consistent with those determined from stimulated cells. For example, the hERG blocker dofetilide significantly prolonged the action potential duration of iPSC-derived cardiomyocytes and induced EADs (see panel below).

Voltage Clamp Assays

Metrion has validated voltage clamp assays to quantify activity of range of ion channels expressed in iPSC-derived ventricular and atrial cardiomyocytes. Metrion can determine the expression density of such currents as part of an in depth service to characterise new cell lines. Voltage clamp studies using either iPSC-derived cardiomyocytes or cell lines expressing recombinant ion channels can also be used to support phenotypic and modelling predications as part of an integrated CiPA approach.