Power spectral analysis of heart rate variability in ryanodine receptor type 3 knockout mice

The role of ryanodine receptor type 3 (RyR-3) in the autonomic control of heart rate (HR) was studied by recording electrocardiogram (ECG) in conscious mutant mice totally lacking RyTR-3 (RyR-3 knockout mice) and their wild-type littermates. In RyR-3 knockout mice. HR was not significantly altered but its variability, evaluated by the coefficient of variance of R-R intervals of ECG, was significantly reduced as compared to that of wild-type mice. Further, sympathetic and vagal control of HR were assessed on the basis of the power spectrum of R-R variability calculated by the autoregressive analysis modified by the maximum entropy method. Low (LF) and high frequency components (HF) and their power, either real values or normalized by total power, were calculated from the power spectrum. In RyR-3 knockout mice, normalized LF power and LF/HF ratio, representing cardiac sympathetic activity and sympatho-vagal balance, respectively, were significantly smaller than in wild-type mice. Additionally, total power and LF power tended to be smaller. These results support the view that insufficient sympathetic control of HR and altered sympatho-vagal balance underlies reduction of HR variability in RyR-3 knockout mice. In conclusion, RyR-3 participates in the physiological control of HR by the cardiac nerve in conscious mice.