The induction of spontaneous repetitive activity by a drive (‘overdrive excitation’) was studied in the sinoatrial node of the guinea pig by recording electrical and mechanical activity in sinoatrial preparations made quiescent by exposure to 20 mM caffeine of caffeine plus high [Ca]₀. Electrical drive induced action potentials that were followed by oscillatory potentials and simultaneous aftercontractions. The oscillatory potentials (and the associated aftercontractions) increased in magnitude with successive action potentials, thereby initiating spontaneous beats during slow drives or after fast drives. The repetitive activity eventually slowed and ceased abruptly as the oscillatory potential failed to attain the threshold. Overdrive induced oscillatory potential and aftercontractions even when it did not initiate spontaneous activity. These results suggest that in the presence of caffeine calcium overload can occur in the sinoatrial node and result in oscillatory potentials and abnormal automaticity.

Keywords:
Sinoatrial node, Caffeine, Calcium overload, Oscillatory potentials, Aftercontraction, Repetitive activity, Guinea pig
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© 1988 S. Karger AG, Basel
1988
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