Abstract 1265 Dexamethasone increases the L-type Ca2+ current in human ventricular cardiomyocytes

Clin Res Cardiol (2022). https://doi.org/10.1007/s00392-022-02002-5
Dexamethasone increases the L-type Ca2+ current in human ventricular cardiomyocytes
B. Pfeilschifter¹, A. Ritzer¹, S. Sommer¹, V. Baron¹, D. Fiegle¹, 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 A large number of studies have shown that glucocorticoid signaling is indispensable for normal cardiac development and function as well as maturation of stem-cell derived cardiomyocytes. Our group recently demonstrated in isolated adult rat cardiomyocytes that glucocorticoids increase inotropy, stabilize excitation-contraction coupling and increase the expression of L-type Ca²⁺ channels as well as the L-type Ca²⁺ current (I_CaL). However, due to methodological limitations it remains unclear if these effects also apply to human cardiomyocytes. To answer this question, we treated human myocardial tissue slices with glucocorticoids for up to one week. Methods Myocardial tissue samples from 12 end-stage heart failure patients were obtained from explanted hearts or the apical tissue accrued during left ventricular (LV) assist device implantation. Using a technique for long-term cardiac tissue culture, slices generated with a vibratome were kept beating in culture for 2 to 8 days and treated with either 100nM dexamethasone (Dex) or vehicle as control. After cultivation, slices were frozen for subsequent qPCR and Western blotting analysis of the CACNA1c subunit of the L-type Ca²⁺ channel or subjected to enzymatic digestion for isolation of individual myocytes. I_CaL was investigated in isolated cardiomyocytes using the ruptured patch whole-cell patch-clamp technique. Results Indicated by adequate contraction in response to electrical stimulation, human myocardial tissue slices were stable in culture. As reported previously, slices treated with dexamethasone exhibited an increased contractile force (F_max = 2070±663 µN) when compared with control slices (F_max = 1030±237 µN, p<0.05). Western blotting of CACNA1c did not reveal a significant increase in protein expression after 7d of Dex treatment. However, Dex caused a 38±6% increase in CACNA1c mRNA after 2d (p<0.01, n=5) and a 23±8% increase after one week (p<0.05, n=8). Importantly, Dex treatment increased I_CaL density by 69% from ‑1.72±0.28 to ‑2.48±0.23 pApF^-1 at V_Pip = 10 mV (p<0.05, n=12 control, n=25 Dex, from 7 slice pairs/patients) without affecting cell capacitance (424±92 vs. 494±60 pF). Conclusions We show that the glucocorticoid dexamethasone significantly increases the expression of the CACNA1c subunit in human ventricular myocardium over the course of one week and causes a striking increase in the L-type Ca²⁺ current. This extents previous findings from animal models and shows that corticosteroid signaling is a potent modulator of the L-type Ca²⁺ current in failing human myocardium. It also suggests increased Ca²⁺entry and subsequently improved excitation-contraction coupling as a main mechanism of glucocorticoid-induced increases in inotropy.
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