Two potentially arrhythmogenic mechanisms of adrenaline action in cardiac muscle.

The effects of rate changes and 'premature' stimulation on the slow inward current of cardiac muscle were studied in the frog atrium. The effects of adrenaline under these conditions was investigated. It was found that adrenaline markedly accelerates the repriming kinetics of the slow inward channel. Adrenaline at low concentrations, sufficient to augment this current, also increases the effect of rate changes. Thus there is a larger second inward current 'staircase' in the presence of adrenaline. It is proposed that the combination of these effects is a possible mechanism by which adrenaline can induce cardiac disorders of rhythm.