Abstract
Autonomic regulation plays a central role in cardiac contractility and excitability in numerous vertebrate species. However, the role of autonomic regulation is less understood in fish physiology. Here, we used Goldfish as a model to explore the role of autonomic regulation. A transmural electrocardiogram recording showed perfusion of the Goldfish heart with isoproterenol increased the spontaneous heart rate, while perfusion with carbamylcholine decreased the spontaneous heart rate. Cardiac action potentials obtained via sharp microelectrodes exhibited the same modifications of the spontaneous heart rate in response to isoproterenol and carbamylcholine. Interestingly, the duration of the cardiac action potentials lengthened in the presence of both isoproterenol and carbamylcholine. To evaluate cardiac contractility, the Goldfish heart was perfused with the Ca2+ indicator Rhod-2 and ventricular epicardial Ca2+ transients were measured using Pulsed Local Field Fluorescence Microscopy. Following isoproterenol perfusion, the amplitude of the Ca2+ transient significantly increased, the half duration of the Ca2+ transient shortened, and there was an observable increase in the velocity of the rise time and fall time of the Ca2+ transient, all of which are compatible with the shortening of the action potential induced by isoproterenol perfusion. On the other hand, carbamylcholine perfusion significantly reduced the amplitude of the Ca2+ transient and increased the half duration of the Ca2+ transient. These results are interesting because the effect of carbamylcholine is opposite to what happens in classically used models, such as mouse hearts, and the autonomic regulation of the Goldfish heart is strikingly similar to what has been observed in larger mammalian models resembling humans.
Highlights
In most vertebrate species, direct input from the autonomic nervous system tightly controls cardiac contractility and excitability (Lee and Shideman, 1959; Katz, 1967; Lindemann and Watanabe, 1985; Cohn, 1989; Henning, 1992)
Goldfish ventricular chronotropic properties were examined via action potential (AP) recordings and spontaneous heart rate recordings (Figure 1)
All kinetic parameters of the AP significantly changed following isoproterenol perfusion; APD30 increased from 228.10 ± 14.40 ms to 237.90 ± 11.80 ms (Figure 2A), APD50 decreased from 353.90 ± 30.40 ms to 300.30 ± 20.00 ms (Figure 2B), and APD90 increased from 455.40 ± 20.10 ms to 468.70 ± 27.00 ms (Figure 2C)
Summary
In most vertebrate species, direct input from the autonomic nervous system tightly controls cardiac contractility and excitability (Lee and Shideman, 1959; Katz, 1967; Lindemann and Watanabe, 1985; Cohn, 1989; Henning, 1992). 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 . This is in part due to humans having strikingly dissimilar action potential (AP) characteristics and electrocardiographic morphology in comparison with commonly used animal. 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. If a fish species does exhibit autonomic regulation, it is likely to be similar to what has been established for many mammalian species
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