Cardiac force-interval relationship, adrenaline and sarcoplasmic reticulum in rainbow trout

The force-interval relationship was examined at 20 and 10 degree C in electrically paced atrial and ventricular tissue of rainbow trout, Oncorhynchus mykiss, regarding dependence on the sarcoplasmic reticulum and influence of adrenaline. In both tissues, adrenaline (10 super(-6) mol/l) doubled control force developed at 0.5 Hz. In atrial but not in ventricular tissue it also shortened the diastolic interval needed for recovery of a given fraction of the control force. In atrial tissue and in ventricular tissue at 20 degree C, the fraction of force recovered in the presence of adrenaline was diminished by 10 mu mol/l of ryanodine, a specific inhibitor of the sarcoplasmic reticulum. In atrial tissue not exposed to adrenaline and in ventricular tissue at 10 degree C irrespective of adrenaline, ryanodine did not affect recovery. In atrial but not in ventricular tissue it also diminished control force. In conclusion, the cardiac sarcoplasmic reticulum of trout seems to support force development during adrenaline dependent increases in heart rate, and in atrial tissue also the force at steady state.