On the mechanisms underlying diastolic voltage oscillations in the sinoatrial node

• Published in: Journal of electrocardiology Vol. 39; no. 3; p. 342
• Main Authors: Catanzaro, John N., Nett, Michael P., Rota, Marcello, Vassalle, Mario
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.07.2006; Elsevier Science Ltd
• Subjects: Action Potentials - physiology; Animals; Biological Clocks - physiology; Caffeine; Calcium overload; Catecholamines; Diastole - physiology; Female; Guinea Pigs; Male; Membrane Potentials - physiology; Oscillatory afterpotential V os; Oscillatory prepotential ThV os; Potassium; Sinoatrial Node - physiology; Sinoatrial node discharge; Tetrodotoxin; Tetrodotoxin; Sinoatrial node discharge; Calcium overload; Catecholamines; Potassium; Oscillatory afterpotential V os; Oscillatory prepotential ThV os; Caffeine
• ISSN: 0022-0736; 1532-8430
• DOI: 10.1016/j.jelectrocard.2006.03.006

The study of the mechanisms underlying the oscillatory afterpotential (V os) and prepotential (ThV os). It has been recently shown that V os and ThV os play an obligatory role in the dominant sinoatrial node (SAN) discharge. Guinea pig isolated SAN was studied in vitro by means of a microelectrode technique. High [K +] o and premature stimuli unmask V os superimposed on early diastolic depolarization and ThV os within a less negative voltage range (“oscillatory zone”). Subthreshold stimuli elicit ThV os in the oscillatory zone, but not at more negative values. Drive and caffeine shift the oscillatory zone in a negative direction. Low caffeine concentrations increase the size of V os and of ThV os, rate, and force. High caffeine concentrations suppress V os but increase the size of ThV os and shift them to more negative values until they eventually miss the threshold. In quiescent SAN in high caffeine, a fast drive enhances ThV os size, thereby initiating a transient spontaneous rhythm (“overdrive excitation”). Adrenergic agonists potentiate caffeine-induced overdrive excitation through an increase in ThV os. In high caffeine, the first twitch after quiescence is not larger, twitch relaxation is slower, V os is abolished, and the prolonged nonoscillatory afterdepolarization V ex is induced, consistent with an impairment of Ca 2+ handling by the sarcoplasmic reticulum. The effects of caffeine in Tyrode's solution are accounted for by the caffeine-induced changes in the oscillatory potentials. Tetrodotoxin decreases force and size of both V os and ThV os. The mechanism underlying V os is related to a diastolic release of Ca 2+ from a Ca 2+-overloaded sarcoplasmic reticulum, whereas that of ThV os appears to be related to ionic currents in the resting potential range that can initiate and sustain spontaneous discharge.