Cardioluminescence in transgenic zebrafish embryos: a Ca2+imaging tool to study drug effects and pathological modeling

The zebrafish embryo has emerged as an excellent model in cardiovascular research. The existing techniques to monitor Ca 2+ in the heart based on fluorescent Ca 2+ biosensors are limited due to phototoxicity and photobleaching. To overcome these issues, we have used bioluminescence. We generated a transgenic line expressing GFP-Aequorin in the heart, Tg ( cmlc2:GA ), and optimized an in vivo aequorin reconstitution protocol to improve the luminescence capacity. This allowed imaging Ca 2+ in long duration recordings in embryos of 3 to 5 days post-fertilization. The analogs diacetyl h -coelenterazine and f -coelenterazine enhanced the light output and signal-to-noise ratio from the embryos. With this cardioluminescence model, we monitored the time-averaged Ca 2+ levels and beat-to-beat Ca 2+ oscillations. Changes in Ca 2+ levels were observed by incubation with BayK8644, an L-type Ca 2+ channel agonist, the channel blocker nifedipine, and β-adrenergic blocker propranolol. Treatment of zebrafish embryos with terfenadine for 24 hours has been proposed as a model of heart failure. Tg ( cmlc2:GA ) embryos treated with terfenadine showed a 2:1 atrioventricular block and a decrease in the ventricular Ca 2+ levels.