Difference in excitation-contraction mechanisms between atrial and ventricular myocardia of hatched chicks

1. Effects of inotropic interventions on contractile force were examined in isolated atrial and ventricular preparations from hatched chicks. 2. The duration of twitch contractions were briefer in the atria than in the ventricle. 3. No difference in the extracellular Ca(2+)-contractile force curve was observed between atrial and ventricular preparations. 4. The sensitivity to nicardipine was higher in the ventricular preparations than in atrial preparations while that to ryanodine was higher in atrial preparations. 5. The magnitude of post-rest contraction was larger than the basal contractile force in atrial preparations, while it was smaller than the basal contractile force in ventricular preparations. 6. These results suggested that the atrial myocardium of hatched chick was more dependent on sarcoplasmic reticulum function than its ventricular myocardium, which is similar to the case with mammalian species.