Quantifying cardiac functions in embryonic and adult zebrafish

Abstract

Zebrafish embryos have been extensively used to study heart development and cardiac function, mainly due to the unique embryology and genetics of this model organism. Since most human heart disease occurs during adulthood, adult zebrafish models of heart disease are being created to dissect mechanisms of the disease and discover novel therapies. However, due to its small heart size, the use of cardiac functional assays in the adult zebrafish has been limited. To address this bottleneck, the transparent fish line casper;Tg(cmlc2:nuDsRed) that has a red fluorescent heart can be used to document beating hearts in vivo and to quantify cardiac functions in adult zebrafish. Here, we describe our methods for quantifying shortening fraction and heart rate in embryonic zebrafish, as well as in the juvenile and adult casper;Tg(cmlc2:nuDsRed) fish. In addition, we describe the red blood cell flow rate assay that can be used to reflect cardiac function indirectly in zebrafish at any stage.

Fig. 1

Orientations and measurement locations for shortening fraction, heart rate, and red blood cell flow rate assays. (a) For cardiac imaging, zebrafish up to 4 weeks old are placed on their right side in 3% methyl cellulose or E3, as shown with the 5-dpf zebrafish. (d) Fish older than 4 weeks are placed on a moist sponge, ventral-side up. (b, c, e and f) Maximum ventricular diastole (VD) and ventricular systole (VS) are shown, with the width depicted as a white dashed line and the length as a black or gray dashed line. Outflow tract (O) and atrium (A) are labeled in images (b, c). For the red blood cell flow rate assay, (g) 5-dpf, (h) 15- and 21 -dpf, and (i) 6-week fish are placed horizontally on their right side. Arrows refer to specific locations used for starting and stopping the stopwatch. Scale bars for (a–i) are 0.25, 0.125, 0.125, 3, 1, 1, 0.5, 0.5, and 0.5 mm, respectively. (Images (g–i) are reproduced from (21)).