The zebrafish (Danio rerio) has been used as a model for studying vertebrate development in the cardiovascular system. In order to monitor heart contraction and cytosolic calcium oscillations, fish were either embedded in methylcellulose or anesthetized with tricaine. Using high-resolution differential interference contrast and calcium imaging microscopy, we here show that dopamine and verapamil alter calcium signaling and muscle contraction in anesthetized zebrafish, but not in embedded zebrafish. In anesthetized fish, dopamine increases the amplitude of cytosolic calcium oscillation with a subsequent increase in heart contraction, whereas verapamil decreases the frequency of calcium oscillation and heart rate. Interestingly, verapamil also increases myocardial contraction. Our data further indicate that verapamil can increase myocardial calcium sensitivity in anesthetized fish. Taken together, our data reinforce in vivo cardiac responses to dopamine and verapamil. Furthermore, effects of dopamine and verapamil on myocardial calcium and contraction are greater in anesthetized than embedded fish. We suggest that while the zebrafish is an excellent model for a cardiovascular imaging study, the cardio-pharmacological profiles are very different between anesthetized and embedded fish.

BackgroundZebrafish have been used as a model for studying vertebrate development and genetics, including the cardiovascular system. Our project aims to monitor heart contraction and cytosolic calcium using a Fura‐2 probe to monitor calcium oscillations with regard to heart contraction.Methods and ResultsUsing high resolution DIC and calcium imaging microscopy, we show that dopamine and verapamil alter calcium signals and muscle contraction in 6‐14 day old anesthetized zebrafish. Dopamine at 100 μg/mL increases heart rate. On the other hand, 40 μg/mL of verapamil decreases heart contraction, but it does not decreases heart rate. Interestingly, no significant difference in calcium in the heart is observed in the zebrafish treated with dopamine or verapamil.ConclusionOur preliminary data indicates that dopamine alters heart rate independent from cytosolic calcium. Furthermore, verapamil decreases heart contraction independent from the changes in cytosolic calcium. We propose here that zebrafish can be used as a model to study cardiovascular functions.