Abstract
Rabbits are an important animal model for the study of cardiac electrophysiology and are suitable for analyzing mechanisms of cardiac arrhythmias. Rabbits are known to have seasonal variation in activity, behavior, and breeding; however, there are few data related to seasonal variation in electrophysiological parameters in the rabbit heart. To determine if there is significant seasonal variation in cardiac electrophysiology of the New Zealand White (NZW) rabbit heart. Male NZW rabbit hearts (N = 55) were purchased from an approved vendor and housed on a 12:12 hr light:dark cycle. Hearts were Langendorff-perfused for simultaneous optical mapping of Vm and Ca2+ with voltage-sensitive (RH237) and calcium-sensitive (Rhod2-AM) indicators, respectively. Data were collected from 2012-2016 and retrospectively analyzed. We defined the seasons meteorologically: December-February as winter, March-May as spring, June-August as summer and September-November as autumn. All data were collected while pacing at a constant cycle length of 300 ms. Retrospective data revealed seasonal variability in the action potential duration (APD) and in the calcium transient duration (CaTD). For summer compared to spring and autumn, APD50 (121.1 ± 11 vs. 137 ± 19.8 and vs. 135.3 ± 11.3 ms, p < 0.01 for both) and APD80 (151.1 ± 11.7 vs. 166.4 ± 17.6 and vs. 163.5 ± 11.9 ms, p < 0.01 for both) were significantly shorter, but not different from winter. For summer compared to spring, CaTD50 (123.8 ± 5.5 vs. 137.7 ± 13.2 ms, p < 0.01) and CaTD80 (162.8 ± 6.1 vs. 178.4 ± 16.9 ms, p = 0.11) were shorter. There was not significance difference in Vm-Ca2+ coupling (i.e., CaTD - APD) between seasons. APD and CaTD are significantly shorter in the summer months of isolated rabbit hearts. These data may provide insight into seasonal patterns of arrhythmia in humans, but should also be considered with regard to experimental rigor and reproducibility.
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