Fig. 3.

The relationships of heart rate variability and redox state in the pacemaker cells of sinoatrial node. The heart rate regulation is very complex and many regulatory mechanisms are involved on different levels. Sympathetic and parasympathetic branches of autonomic nervous system play a major role in modulation of heart automaticity, however intrinsic metabolic and electrophysiological properties of sinoatrial node cardiocytes may be crucial for the amplitude of heart rhythm oscillations. Higher activity of Na⁺/K⁺ ATPase powered by sufficient ATP supply provide diastolic hyperpolarization of the membrane of cardiocyte, decreasing excitability and promoting vagal brake effect (providing heart rate decelerations). Energetic deficit, in contrast, provides depolarization of membrane, increased excitability and lower amplitude of heart rhythm oscillations.