Clin Res Cardiol (2023). https://doi.org/10.1007/s00392-023-02180-w

Electrophysiological effects of dexamethasone on human ventricular cardiomyocytes

B. Pfeilschifter1, D. Fiegle1, A. Ritzer1, S. Sommer1, V. Baron1, C. Heim2, M. Weyand2, H. Milting3, T. Seidel1, T. Volk1

1Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen; 2Herzchirurgische Klinik, Universitätsklinikum Erlangen, Erlangen; 3E.& H. Klessmann-Institut f. kardiovask. Forschung, Herz- und Diabeteszentrum NRW, Bad Oeynhausen;

Background Glucocorticoid signaling is important for normal cardiac development and function and has been shown to improve maturation of stem-cell derived cardiomyocytes. We demonstrated previously that glucocorticoids elongate APD and increase L-type Ca2+ current (ICaL) in isolated adult rat cardiomyocytes. Furthermore, we found increased contractility and increased expression of L-type Ca2+ channels in human myocardium treated with glucocorticoids. Here, we investigated how glucocorticoids influence transmembrane currents in human ventricular myocardial slices.   Methods Vibratome-cut slices from end-stage failing human heart samples were kept in beating culture for 2 to 8 days, either with 100 nM dexamethasone (DEX) or vehicle as glucocorticoid-free control (CTRL). After cultivation, slices were frozen for qPCR or used immediately for cell isolation to measure ionic currents and action potentials (AP) using the ruptured patch whole-cell patch-clamp configuration. Results Dexamethasone treatment increased Ito at VPip = 60 mV 2.7fold from 2.2 to 5.8 pApF-1 (p<0.001, n (cells) = 21 / N (samples) = 6 DEX, n=21 / N=6 CTRL). Voltage dependent inactivation of Ito was not different (V50 = -33.4±0.9 mV DEX, -32.7±0.7 mV CTRL) nor was time dependent recovery (τ1 = 86.0±4.8 ms, τ2 = 4165±322 ms DEX; τ1 = 70.7±7.4 ms τ2 = 3930±481 ms CTRL). Recovery from inactivation of Ito was also unaffected. The inwardly rectifying K+ current at VPip = -120 mV was increased 1.5fold from -1.75±0.2 pApF-1 in CTRL to -2.68±0.3 pApF-1 in DEX-treated myocytes (p<0.01, n=19 / N=5 DEX, n=18 / N=5 CTRL). Furthermore, ICaL amplitude increased markedly upon DEX treatment (-2.5±0.2 pApF-1 DEX vs -1.65±0.17 pApF-1 CTRL, p<0.01). DEX myocytes exhibited larger membrane capacitance than CTRL cells (p<0.01, 432±28 pF, n= 71 DEX, 327±27 pF, n=60 CTRL). Resting membrane potential was slightly more negative in DEX than in CTRL ( 84.25±0.5 vs -86.16±0.5 mV, p<0.01, n=14 / N=5 DEX, n =13 / N=3 CTRL), while APs in DEX showed a trend towards shorter values (p=0.19, APD90 = 988.5±123.2 ms DEX and 1216.8±85.7 ms CTRL). Fitting to these results, relative mRNA expression of the ion channel subunits underlying the ionic currents investigated, were increased in DEX vs CTRL: CACNA1c (1.2fold, p<0.05), KCND3 (1.4fold, p<0.05), KCNIP2 (7.6fold, p<0.01), KCNJ2 (1.8fold, p<0.001) and KCNJ4 (1.5fold, p<0.05). Conclusions Dexamethasone increases current densities of ICaL, Ito and IK1 in human failing myocardium without affecting kinetic parameters, and slightly hyperpolarizes maximum diastolic potential. It also increases the expression of the respective ion channel subunits. In contrast to isolated rat myocytes, no AP prolongation was found, possibly a result of increased K+ currents opposing the effects of increased ICaL. Collectively, these effects seem to oppose the cellular electrophysiological changes commonly observed in heart failure and presumably contribute to increased contractility and excitability we observe in human myocardium treated with dexamethasone in vitro.

https://dgk.org/kongress_programme/jt2023/aP2219.html