Functional Assessment of Cardiac Responses of Adult Zebrafish (Danio rerio) to Acute and Chronic Temperature Change Using High-Resolution Echocardiography

The zebrafish (Danio rerio) is an important organism as a model for understanding vertebrate cardiovascular development. However, little is known about adult ZF cardiac function and how contractile function changes to cope with fluctuations in ambient temperature. The goals of this study were to: 1) determine if high resolution echocardiography (HRE) in the presence of reduced cardiodepressant anesthetics could be used to accurately investigate the structural and functional properties of the ZF heart and 2) if the effect of ambient temperature changes both acutely and chronically could be determined non-invasively using HRE in vivo. Heart rate (HR) appears to be the critical factor in modifying cardiac output (CO) with ambient temperature fluctuation as it increases from 78 ± 5.9 bpm at 18°C to 162 ± 9.7 bpm at 28°C regardless of acclimation state (cold acclimated CA– 18°C; warm acclimated WA– 28°C). Stroke volume (SV) is highest when the ambient temperature matches the acclimation temperature, though this difference did not constitute a significant effect (CA 1.17 ± 0.15 μL at 18°C vs 1.06 ± 0.14 μl at 28°C; WA 1.10 ± 0.13 μL at 18°C vs 1.12 ± 0.12 μl at 28°C). The isovolumetric contraction time (IVCT) was significantly shorter in CA fish at 18°C. The CA group showed improved systolic function at 18°C in comparison to the WA group with significant increases in both ejection fraction and fractional shortening and decreases in IVCT. The decreased early peak (E) velocity and early peak velocity / atrial peak velocity (E/A) ratio in the CA group are likely associated with increased reliance on atrial contraction for ventricular filling

Investigating the Utility of Adult Zebrafish Ex Vivo Whole Hearts to Pharmacologically Screen hERG Channel Activator Compounds

There is significant interest in the potential utility of small molecule activator compounds to mitigate cardiac arrhythmia caused by loss-of-function of hERG1a voltage-gated potassium channels. Zebrafish (Danio rerio) have been proposed as a cost effective, high throughput drug-screening model to identify compounds that cause hERG1a dysfunction. However, there are no reports on the effects of hERG1a activator compounds in zebrafish, and consequently on the utility of the model to screen for potential gain-of-function therapeutics. Here, we examined the effects of hERG1a blocker, and type 1 and type 2 activator, compounds on isolated zkcnh6a (zERG3) channels in the Xenopus laevis oocyte heterologous expression system, as well as action potentials recorded from ex vivo adult zebrafish whole hearts using optical mapping. Our functional data from isolated zkcnh6a channels show that these channels respond to hERG1a channel blockers (dofetilide and terfenadine), and type 1 (RPR260243) and type 2 (NS1643, PD-118057) hERG1a activator compounds, in a similar manner to hKCNH2a channels, with minor differences largely accounted for by subtly different biophysical properties in the two channels. In ex vivo zebrafish whole hearts, two of the three hERG1a activators examined caused abbreviation of the APD, while hERG1a blockers caused APD prolongation. These data represent, to our knowledge, the first pharmacological characterization of isolated zkcnh6a channels and the first assessment of hERG enhancing therapeutics in zebrafish. Our findings suggest that the zebrafish ex vivo whole heart model serves as a valuable tool in the screening of hKCNH2a blocker and activator compounds

Correction: Functional Assessment of Cardiac Responses of Adult Zebrafish (<i>Danio rerio</i>) to Acute and Chronic Temperature Change Using High-Resolution Echocardiography

Correction: Functional Assessment of Cardiac Responses of Adult Zebrafish (<i>Danio rerio</i>) to Acute and Chronic Temperature Change Using High-Resolution Echocardiograph

Longitudinal position of zebrafish.

<p>The ultrasound transducer beam (70 MHz) was positioned at about 85 degrees to ventral surface of the anesthetized zebrafish through all protocols. ZF were placed in a 45 ml custom-made water-jacketed glass chamber with the thermal probe (shown with the blue wire) inserted into the bath in proximity to the ZF.</p

B-mode image of a long-axis view of a WA ZF heart at 28°C.

<p>The perimeter of the ventricle represented by (A) red trace for diastole and (B) cyan trace for systole. V Area, ventricular area; V, volume; Ld, greatest length of the spline during diastole; Ls, greatest length of the splice during systole; SV, stroke volume determined by diastolic volume-systolic volume; EF, ejection fraction determined by SV/diastolic volume; FS, fractional shortening determined by (Ld—Ls) / Ld * 100.</p

Parameters were calculated from pulse wave Doppler mode of ventricular inflow view (n = 10).

<p>(A) Early (e) filling peak velocity, (B) atrial (a) flow peak velocity, (C) E/A ratio and (D) isovolumic contraction time (IVCT) of CA and WA zebrafish at two acute temperatures. The ratio of early (e) filling peak velocity and atrial (a) late filling peak velocity allows for evaluation of zebrafish ventricular function. Error bars represent SEM. * represents significant difference of both groups between temperatures. † represents significant interacting effect of acclimation state. Red: warm acclimated (WA) zebrafish. Blue: cold acclimated (CA) zebrafish.</p