Abstract

The study of myocardial transmembrane ion currents is fundamental to understand frequent pathologies such as arrhythmias and ischemia. Conventional electrocardiography (ECG) is not able to record ion currents, while the use of intracellular microelectrodes in a beating heart has technical limitations. Myocardial monophasic action potentials (MAPs) recorded with suction electrodes allow the evaluation of ionic currents similar to those recorded by intracellular glass microelectrodes. The technique is based on the fact that suction, through a small diameter tube, on the myocardial cell, induces an opening at the membrane, connecting the intracellular media to the electrode by a saline bridge. The electrophysiology of zebrafish heart is remarkably similar to the human; however, in situ evaluation of MAPs has not been yet explored. In this study, we aimed to establish a myocardial MAP recording technique for adult zebrafish. Male adult wild-type zebrafish were anesthetized and 50% of the beating ventricle was exposed. A glass hematocrit capillary tube (1.1 mm inner diameter) was used as a suction electrode connected to a 3-way stopcock valve, which is also connected to a syringe containing a chloride-coated silver wire for signal recording. Gentle suction was exerted by a syringe filled with ringer and connected to the 3-way stopcock valve. Two needles were used for ground (tail) and indifferent (abdomen) electrodes. Without suction, the system can record conventional ECG, but applying suction MAPs are registered and show typical morphology with phase 0-4 sequence. MAP amplitude and duration values show low variability. Ischemia and/or lidocaine-induced Na+ channel blocking dramatically reduced MAP amplitude. These results strongly suggest that the suction electrode technique is a promising method to record myocardial ion currents in situ in zebrafish.