P2559The mechanisms of spontaneous action potential generation in sinoauricular valve of the chick embryos
Authors: Golovko A , Gonotkov M , Lebedeva E 
Published: October 2019

Abstract

Background
The changes in the density of ion channels and/or damage of ion channel proteins violates the homeostasis of the potential forming ions in myocardium cells and may contribute to arrhythmogenesis. The study of ion channel function in embryos is important in order to understand the mechanisms of arrhythmia.
The purpose of the present study was to identify the key ion channels that form action potentials (APs) in pacemaker cells in the area of the sinoauricular (SA) chicken embryo valve.

Material and methods
The embryos were removed from fertilized White Leghorn breed chicken eggs on the 10±1 day of incubation (ED10). The experiments were performed on freshly prepared strips (3 mm × 2 mm) of the right atrium, which included the left SA valve itself as well as the surrounding tissue. After that the APs were recorded from the area of left SA valve using the microelectrode technique. The functional analysis of ion channels was performed using the specific ion channel blockers.

Results
The strips generated APs with slow diastolic depolarization (SDD) and frequency from 132 to 251 impulses per min (ipm) (average - 177±22 ipm). The APs amplitude and dV/dtmax were 102±9 mV and 98±25 V/s (nstrips=49). At the third minute of exposure to E-4031 (1 μmol), a blocker of rapid outward K-current channels, IKr, the increase in the duration of the AP repolarization phase by 30% and the shortening of SDD by 20–25% (p<0.05; n=6) were registered. The APs generation frequency increased by 10%. Subsequently we observed the monotonic decrease in the AP amplitude due to the reduced overshoot and depolarized Emax. The electrical activity of all strips was blocked on the 20±2 min (Fig.1.a-c). Lidocaine (500 μmol), a blocker of Nav1.5 channels, increased a duration of SDD and APD90 twice, but decreased dV/dtmax by 2.5 times. The APs generation frequency decreased by 30% in comparison to the control. After 8±2 min exposure to lidocaine, the APs generation was blocked in 56% of samples. It is important to mention that in these strips right before the APs generation was blocked dV/dtmax was 30±15 V/s. In the samples, where the APs were not blocked after the exposure to lidocaine this parameter was 14±10 V/s (Fig. 1d-e). Nifedipine (10 μmol), a blocker of L-type Ca2+-channels, decreased APD90 by 56% and SDD by 25%. The APs generation frequency increased twice in comparison to the control samples (fig.1f-h). The chronotropic effects of nifedipine were dose-dependent. Nifedipine did not induce the blocking of APs generation.
Figure 1. Effects of E-4031 (a-c), lidocaine (d-e) and nifedipine (e-g) on APs.

Conclusions
The received data demonstrate that the key role in the APs formation in ED10 embryos belong to the outward IKr and inward INa, but not to ICa,L. Thus, the mechanisms of spontaneous action potential generation in ED10 chick embryos have more in common with that in human iPSC-derived cardiomyocytes rather than in SA area cells of the ED11 mice embryos.

Acknowledgement/Funding
Rus fund Basic Research No. 18-34-00654; Project RAS No. 0415-2019-0006 and No. AAAA-A17-117012310152-2