[Phasic and tonic components of mechanical tension in the myocardium of the atria and ventricle of the frog].

The complex mechanical response of the frog atria to sustained depolarizing current were divided into three components: T1--owing to slow inward calcium current; TII--related to calcium release from intracellular sources; and TIII--related to potential--dependent sodium-calcium exchange diffusion. Differences in electromechanical coupling of the frog atrium and ventricle myocardium, are discussed.