Assessing Sex and Sex Steroid Influence on Cardiac Electrophysiology in Cultured Monolayers

Abstract

A link exists between atrial fibrillation and the extent of pericardial adipose accumulation. The underlying mechanisms are poorly understood. Regional adipose depots highly express aromatase, converting androgens to oestrogens. We recently showed pericardial adipose expresses aromatase, and that augmented local oestrogen biosynthetic capacity in pericardial adipose was linked with increased atrial arrhythmia vulnerability. The aim of this study was to optimise cultured cardiac monolayer plating conditions on multi-electrode array (MEA) chips, and assess the effect of sex and sex steroids on cardiac conduction properties. Neonatal rat ventricular myocytes (NRVMs; male/female separately or combined) were enzymatically isolated and cultured on MEA chips (72 h). Extracellular recordings were performed in the presence/absence of 1 μM isoproterenol. Additional monolayers were treated with 100 nM testosterone (72 h) and electrophysiological responses recorded. Cardiac monolayers exhibited stable electrophysiological recordings over 35 minutes. Isoproterenol significantly increased spontaneous beating rate (90 ± 6 to 138 ± 14 bpm; p < 0.05 [n = 4]) and conduction velocity (22.25 ± 1.70 to 24.42 ± 1.54 cm/s; p < 0.05), and decreased field potential duration (155.1 ± 9.1 to 105.6 ± 8.8 ms; p < 0.05). No differences in basal electrical properties or isoproterenol responses were detected between male and female NRVM cultures. Testosterone significantly increased conduction velocity (17.85 ± 1.06 vs 14.39 ± 1.13 cm/s [n = 7 vs n = 12; p < 0.05]), with no effect on beating rate or field potential duration. This study validates the use of combined male/female NRVM cultures in MEA studies. Our findings also indicate testosterone influences conduction properties. Further studies will now assess the actions of oestrogens and evaluate how pericardial adipose regulates the local androgen/estrogen balance to influence conduction heterogeneity and arrhythmia vulnerability.