Role of Heart Rate, Temperature, and Autonomic Nervous System Regulation in the Cardiac Action Potential and Calcium Handling Dynamics in an Intact Goldfish Heart
In the last decade alone fish hearts have become an increasingly popular model for studying heart function. Although fish hearts contain a single atrium and ventricle and present a fundamentally different cardiovascular system when compared to mammalian models, there are many developmental, structural, and functional commonalities between the two vertebrate classes. The goldfish heart, specifically, has remarkably similar electrical properties to that of humans’. For example, the heart rate, action potential morphology, and Ca2+ transient kinetics and dynamics of adult goldfish closely parallel those of humans, even more so than mice. In nearly all vertebrate species, direct input from the autonomic nervous system tightly controls cardiac contractility and excitability. Although there is an abundant amount of research on the autonomic control of cardiac contractility and excitability in numerous mammalian species, the characterization of pathophysiological mechanisms is still difficult to obtain for humans specifically. This is in part due to humans having strikingly dissimilar AP characteristics and electrocardiographic morphology in comparison to commonly used animal models such as mice, rats, and rabbits. Fish, on the other hand, are the largest and most diverse group of vertebrates, and as such, their autonomic nervous system regulation can often deviate from the classical vertebrate models used to study autonomic control of cardiac contractility and excitability. Ventricular APs, electrocardiograms, and Ca2+ transients recorded from the goldfish intact heart showed perfusion with either 100 nM isoproterenol (sympathetic agonist) or 5 µM carbamylcholine (parasympathetic agonist), was enough to stimulate the sympathetic branch or parasympathetic branch, respectively. Interestingly, our results indicate stimulation of the goldfish autonomic nervous system by these commonly used agonists resulted in a corresponding change in cardiac dromotropism, chronotropism, ionotropism, and lusitropism in a similar manner observed in humans. The data obtained from our experiments have led us to propose the goldfish heart as an excellent model for performing physiological experiments at the intact-heart level. Moreover, its shared ionic and electrical similarities with larger mammals open a new avenue for goldfish hearts to be used as a model to study human physiology.