Large-Scale Contractility Measurements Reveal Large Atrioventricular and Subtle Interventricular Differences in Cultured Unloaded Rat Cardiomyocytes

Abstract

The chambers of the heart fulfill different hemodynamic functions, which are reflected in their structural and contractile properties. While the atria are highly elastic to allow filling from the venous system, the ventricles need to be able to produce sufficiently high pressures to eject blood into the circulation. The right ventricle (RV) pumps into the low pressure pulmonary circulation, while the left ventricle (LV) needs to overcome the high pressure of the systemic circulation. It is incompletely understood whether these differences can be explained by the contractile differences at the level of the individual cardiomyocytes of the chambers. We addressed this by isolating cardiomyocytes from atria, RV, LV, and interventricular septum (IVS) of five healthy wild-type rats. Using a high-throughput contractility setup , we measured contractile function of 2,043 cells after overnight culture. Compared to ventricular cardiomyocytes, atrial cells showed a twofold lower contraction amplitude and 1.4-to 1.7-fold slower kinetics of contraction and relaxation. The interventricular differences in contractile function were much smaller; RV cells displayed 12-13% less fractional shortening and 5-9% slower contraction and 3-15% slower relaxation kinetics relative to their LV and IVS counterparts. Aided by a large dataset, we established relationships between contractile parameters and found contraction velocity, fractional shortening and relaxation velocity to be highly correlated. In conclusion, our findings are in line with contractile differences observed at the atrioventricular level, but can only partly explain the interventricular differences that exist at the organ level.

Type 1 Diabetes Impairs Cardiomyocyte Contractility in the Left and Right Ventricular Free Walls but Preserves It in the Interventricular Septum

“…Our study demonstrates that in the healthy heart, CM from LV, RV, and IS differ in morphology, Ca 2+ handling, and contractile function. We have shown that the contractile function of IS myocytes is closer to that of LV and distinct from the contractile function of RV, according to [37]. In mechanically non-loaded conditions, CM from RV had a smaller amplitude of sarcomere shortening and shorter times of shortening and relaxation than IS, which agrees with [37].…”

“…We have shown that the contractile function of IS myocytes is closer to that of LV and distinct from the contractile function of RV, according to [37]. In mechanically non-loaded conditions, CM from RV had a smaller amplitude of sarcomere shortening and shorter times of shortening and relaxation than IS, which agrees with [37]. However, we have not found any significant differences in the amplitude of sarcomere shortening between CM from LV and RV as observed in rodents in earlier studies [37][38][39].…”

Automatic detection of adult cardiomyocyte for high throughput measurements of calcium and contractility

“…This increased the throughput of these measurements considerably. Wright et al shows that this improves the data quality, enabling inter-preparation and within-preparation statistical correction which results in more reliable hypothesis testing [ 13 , 24 ].…”

“…The current validation was performed on rat cardiomyocytes, but Wright et al also shows its potential in mouse, guinea pig and human cardiomyocytes [ 13 ]. The increased throughput reduces the number of animals needed, the standardized conditions reduce variability between animals, and the increased number of measurements per drug result in more reliable outcomes [ 12 , 13 , 24 ].…”

“…This balance can change between projects, as it depends on the quality of the cells. Additionally, the acquired data can be filtered by applying exclusion criteria on for example the number of transients, baseline sarcomere length or goodness of transient fitting in CytoSolver [ 24 ].…”