...). Acetylcholine (ACh) reduced or abolished these events, an action which was blocked by atropine. Norepinephrine exaggerated the effects of overdrive, and ACh markedly antagonized such an enhancement. Caffeine at low concentrations increased both I os and I ex whereas at high concentrations caffeine abolished I...

... by exposure to 20 m M 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...