Electrophysiology of Zebrafish Embryonic Hearts

The heart of zebrafish embryos 3 days after fertilization was dissected from the thorax en bloc by using fine forceps and transferred to the recording chamber. Only spontaneously beating whole hearts were studied. All experiments were performed at room temperature. The recording chamber was superfused with a solution containing 140 mM NaCl, 4 mM KCl, 1.8 mM CaCl₂, 1 mM MgCl₂, 10 mM glucose and 10 mM Hepes (pH 7.4)19 (link)37 (link). Action potentials were recorded by using the microelectrode and disrupted patch method19 (link)37 (link). Atrial action potentials were measured by using an amplifier (Axopatch 200B; Axon Instrument, USA) and digitized with a 12-bit analogue-to-digital converter (Digidata 1440A Interface; Molecular Devices, USA). Resting action potentials were first validated and then triggered by incrementally injecting pulses of depolarizing current or field pacing. APD was measured at 90% repolarization37 (link)38 (link).