Effects of caffeine and isoprenaline on mammalian ventricular muscle

Abstract

1 Caffeine, 0·6–20·0 mm, altered the duration of the action potential recorded from kitten papillary muscles; low concentrations shortened and high concentrations prolonged the action potential. 2 Caffeine, 20 mm, prolonged the action potential by delaying the final phase of repolarization. 3 Caffeine, 2·0–20·0 mm increased the tension developed and the duration of the isometric contraction. 4 When large stimulating electrodes were used, all concentrations of caffeine increased the duration of the action potential; this effect was probably due to the interactions of caffeine and released endogenous catecholamines. 5 Concentrations of caffeine and isoprenaline, which separately caused little change in the duration of the action potential, greatly prolonged the action potential when used together. 6 The effects of caffeine may be due to an increase in membrane calcium current in addition to an action on intracellular calcium stores.