Stretching-induced changes in the action potential of the atrial myocardium.

The paper reports on changes of the configuration of the action potential recorded from atrial trabecular preparations of the rabbit. Trabeculae, which were isolated from the right atrial cavum (initial length between 2.6 and 5.4 mm) were stretched up to 160% of the initial length. After stretching the steady state action potentials were analysed. While increasing the trabecular length, the duration of 90% repolarization was prolonged and the duration of 25% repolarization was shortened drastically. The conductance for a time-independent potassium outward current gK, measured from the trajectories of the repolarization phase of the action potential, was reduced by increasing the trabecular length. The reconstruction of the measured action potential suggests an increased anomalous rectification for the time-independent potassium current, a decreased amount of the inward transported calcium during the action potential, and a more rapid inactivation of the Ca++-inward current by stretching the atrial myocardium. The results concerning the gK and the anomalous rectification for the potassium current may explain the alleviated generation of the extrasystoles and arrhythmias in the stretched atrial myocardium. The reduction of the Ca++-transport during the action potential may be a control mechanism protecting the heart tissue from the destabilizing effect of an increased anomalous rectification for a time-independent potassium current.