Specific electromechanical responses of cardiomyocytes to individual and combined components of ischemia

Abstract

The main factors of myocardial ischemia are hypoxia, substrate deprivation, acidosis, and high extracellular potassium concentration ([K+]e), but the influence of each of these factors has not yet been evaluated in a cardiomyocyte (CM) culture system. Electromechanical responses to the individual and combined components of ischemia were studied in CM cultured from newborn rat ventricles. Action potentials (APs) were recorded using glass microelectrodes and contractions were monitored photometrically. Glucose-free hypoxia initially reduced AP duration, amplitude, and rate and altered excitation-contraction coupling, but AP upstroke velocity (Vmax) remained unaffected. Early afterdepolarizations appeared, leading to bursts of high-rate triggered impulses before the complete arrest of electromechanical activity after 120 min. Acidosis reduced Vmax whereas AP amplitude and rate were moderately decreased. Combining acidosis and substrate-free hypoxia also decreased Vmax but attenuated the effects of substrate-free hypoxia on APs and delayed the cessation of the electrical activity (180 min). Raising [K+]e reduced the maximal diastolic potential and Vmax. Total ischemia (substrate deletion, hypoxia, acidosis, and high [K+]e) decreased AP amplitude and Vmax without changing AP duration. Moreover, delayed afterdepolarizations appeared, initiating triggered activity. Ultimately, 120 min of total ischemia blocked APs and contractions. To conclude, glucose-free hypoxia caused severe functional defects, acidosis delayed the changes induced by substrate-free hypoxia, and total ischemia induced specific dysfunctions differing from those caused by the former conditions. Heart-cell cultures thus represent a valuable tool to scrutinize the individual and combined components of ischemia on CMs.

Multisite field potential recordings and analysis of the impulse propagation pattern in cardiac cells culture

“…Experimental model are thus mandatory to get relevant insights into this kind of arrhythmogenesis. We confirmed here that cardiac muscle cells cultivated from newborn rat hearts display differentiated functional properties, and therefore represent a valuable cellular model of the myocardial excitability, as demonstrated earlier [5,6].…”

“…1), as previously described. This observation confirmed that these cells display differentiated functions that were very similar to those of mature cardiac muscle cells [5]. The action potentials were regularly coupled to synchronous cell shortening, with a highly constant time delay between the action potential and the contraction.…”

“…Experimental model are thus mandatory to get relevant insights into this kind of arrhythmogenesis. We confirmed here that cardiac muscle cells cultivated from newborn rat hearts display differentiated functional properties, and therefore represent a valuable cellular model of the myocardial excitability, as demonstrated earlier [5,6].To provide further insights into the impulse propagation between cardiac myocytes, we performed multiparametric studies of excitation spread in confluent monolayers of cultured cardiomyocytes (CM) using either simultaneous paired intracellular microelectrodes or microelectrode arrays (MEA). The section 2 describe the materials and methods used in our study, the section 3 shows some results and then the last section 4 is devoted to the conclusion and discussion.…”

“…CM cultures were mounted in a thermo-controlled (37 • C) bath on an inverted microscope as previously described [5]. Simultaneous paired intracellular recordings of action potentials in two individual CM spaced 100-300 µm apart were done using two independently driven conventional glass microelectrodes.…”

“…The contractions were simultaneously recorded by the use of a video cell motion detector [6]. The electromechanical signals were acquired, stored and analyzed as reported previously [5].…”