Excitation-contraction coupling in zebrafish ventricular myocardium is regulated by trans-sarcolemmal Ca2+ influx and sarcoplasmic reticulum Ca2+ release.
Zebrafish (Danio rerio) have become a popular model in cardiovascular research mainly due to identification of a large number of mutants with structural defects. In recent years, cardiomyopathies and other diseases influencing contractility of the heart have been studied in zebrafish mutants. However, little is known about the regulation of contractility of the zebrafish heart on a tissue level. The aim of the present study was to elucidate the role of trans-sarcolemmal Ca(2+)-flux and sarcoplasmic reticulum Ca(2+)-release in zebrafish myocardium. Using isometric force measurements of fresh heart slices, we characterised the effects of changes of the extracellular Ca(2+)-concentration, trans-sarcolemmal Ca(2+)-flux via L-type Ca(2+)-channels and Na(+)-Ca(2+)-exchanger, and Ca(2+)-release from the sarcoplasmic reticulum as well as beating frequency and β-adrenergic stimulation on contractility of adult zebrafish myocardium. We found an overall negative force-frequency relationship (FFR). Inhibition of L-type Ca(2+)-channels by verapamil (1 μM) decreased force of contraction to 22 ± 7% compared to baseline (n=4, p<0.05). Ni(2+) was the only substance to prolong relaxation (5 mM, time after peak to 50% relaxation: 73 ± 3 ms vs. 101 ± 8 ms, n=5, p<0.05). Surprisingly though, inhibition of the sarcoplasmic Ca(2+)-release decreased force development to 54 ± 3% in ventricular (n=13, p<0.05) and to 52 ± 8% in atrial myocardium (n=5, p<0.05) suggesting a substantial role of SR Ca(2+)-release in force generation. In line with this finding, we observed significant post pause potentiation after pauses of 5 s (169 ± 7% force compared to baseline, n=8, p<0.05) and 10 s (198 ± 9% force compared to baseline, n=5, p<0.05) and mildly positive lusitropy after β-adrenergic stimulation. In conclusion, force development in adult zebrafish ventricular myocardium requires not only trans-sarcolemmal Ca2+-flux, but also intact sarcoplasmic reticulum Ca(2+)-cycling. In contrast to mammals, FFR is strongly negative in the zebrafish heart. These aspects need to be considered when using zebrafish to model human diseases of myocardial contractility.
Department of Paediatric Cardiology, Cologne Heart Centre, Medical Faculty, University of Cologne, Cologne, North Rhine-Westphalia, Germany.
Moritz
M
Haustein
Department of Paediatric Cardiology, Cologne Heart Centre, Medical Faculty, University of Cologne, Cologne, North Rhine-Westphalia, Germany; Institute for Neurophysiology, Medical Faculty, University of Cologne, Cologne, North Rhine-Westphalia, Germany.
Tobias
T
Hannes
Institute for Neurophysiology, Medical Faculty, University of Cologne, Cologne, North Rhine-Westphalia, Germany.
Jan
J
Trieschmann
Institute of Physiological Chemistry, University Hospital Essen, Essen, North Rhine-Westphalia, Germany.
Rabea
R
Verhaegh
Institute for Neurophysiology, Medical Faculty, University of Cologne, Cologne, North Rhine-Westphalia, Germany.
Annette
A
Köster
Institute for Neurophysiology, Medical Faculty, University of Cologne, Cologne, North Rhine-Westphalia, Germany.
Jürgen
J
Hescheler
Department of Paediatric Cardiology, Cologne Heart Centre, Medical Faculty, University of Cologne, Cologne, North Rhine-Westphalia, Germany.
Konrad
K
Brockmeier
Department of Paediatric Cardiology, Cologne Heart Centre, Medical Faculty, University of Cologne, Cologne, North Rhine-Westphalia, Germany.
Roland
R
Adelmann
Department of Paediatric Cardiology, University Hospital of Giessen and Marburg, University of Giessen and Marburg, Giessen, Hessen, Germany.
Markus
M
Khalil
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects; D056966:Excitation Contraction Coupling / Q000187:drug effects / Q000502:physiology*; D005110:Extracellular Space / Q000378:metabolism; D006352:Heart Ventricles / Q000187:drug effects / Q000378:metabolism*; D007150:Immunohistochemistry; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology; D009206:Myocardium / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D013696:Temperature; D015027:Zebrafish
D000318:Adrenergic beta-Agonists; D015220:Calcium Channels; D002118:Calcium