Influence of caffeine on force development and force-frequency relations in cat and rat heart muscle

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Abstract
The effects of caffeine on isometric force development and force-frequency relationships were compared in cat and rat papillary muscle preparations. The frequency of contraction determined whether caffeine augmented or diminished contractile force in cat muscles, but caffeine depressed contractions under all conditions in rat muscles. The time course of contraction and relaxation was slowed in both species by 10 mM caffeine but slightly abbreviated by 1 mM caffeine in the rat. The onset of the effects of caffeine was equally rapid in both species. Caffeine abolished post extrasystolic potentiation in both species and caused paradoxical post extrasystolic depression in rat muscles.