Abstract
The influence of various calcium concentrations and of the beta-sympathomimeticum orciprenaline (Alupent) on the force-frequency relationship and on the resting potentiation of isolated isometrically contracting papillary muscles of the guinea pig heart was studied. Elevation of Ca concentration and/or addition of orciprenaline augment the amplitudes of contractions elicited by rhythmical stimulation, but they diminish the amplitudes of test contractions elicited after a test interval of 1-2 s. It is suggested that calcium and orciprenaline strengthen the calcium loss from the sarcoplasmic reticulum out of the cell during a prolonged interval.