Cardiomyocyte Pacing

Many compounds exhibit use-dependent effects. Reverse use-dependence, which occurs when a compound produces greater effects at slower beat rates, is an important indicator of proarrhythmic risk. The dedicated E-Stim+ electrode allows the user to systematically vary beat rate to identify such use dependent effects. Thus, pacing with the E-Stim+ electrode significantly increases the information content of your assay.

(D) Reverse use-dependence of E-4031, a hERG channel blocker, revealed by pacing Pluricyte® Cardiomyocytes with the E-Stim+ electrode. (E) Use dependence of TTX, a sodium channel blocker, revealed by pacing Pluricyte Cardiomyocytes with the the E-Stim+ electrode. (D,E) Bars represent mean ± 1 standard error of the mean. Numbers above the bars indicate the number of wells successfully paced.

Cardiac repolarization is intrinsically linked to the beat frequency, both of which are sensitive to pharmacological manipulation. Optogenetic stimulation can be used to control the beat frequency and remove it as a variable, resulting in increased reliability of the repolarization measurement.

(F, G) The beat rate of Pluricyte^® Cardiomyocytes was increased in a step-wise manner (known as a “chirp” assay). The field potential duration (FPD) adapted with each sequential beat rate increase up to 3 Hz. (H) Typical clinical correction formulas, the Fridericia and Bazzett, did not accurately predict the FPD. However, pacing with the Lumos revealed the cell-specific beat rate correction relationship.

Optogenetic stimulation in conjunction with LEAP can be used to quantify prolongation independent of beat period and quantify rate-dependent drug effects.

HiPSC-cardiomyocytes were transduced with channel rhodopsin 2 (ChR2), and pulses of blue light from the Lumos were used to pace cardiomyocytes at successively faster rates. Here, sotalol causes reverse use-dependent prolongation, resulting in longer prolongation at a slower beat rate.

Getting started with Maestro Pro and Edge couldn't be easier. Culture your cardiomyocytes in an Axion multiwell MEA plate (Day 0). For optogenetic experiments, using adeno-associated virus-based vectors, add the virus to the cell suspension at the time of plating.  Allow 7-14 days for opsin expression.  When transfecting cardiomyocytes with mRNA-based opsins, transfect at peak cardiomyocyte activity and allow 2 days for opsin expression.  Load the MEA plate into the Maestro MEA system at the desired recording times and begin recording.  Perform optical stimulation experiments using the Lumos optical stimulator, or electrical stimulation studies using any of the microelectrodes in the wells of the MEA plate (Day 7+).  Analyze the cardiomyocyte activity with AxIS Navigator Cardiac Module software.