Polyamines have been shown to be present in many cell types and their concentration on within the tissue changes in response to a variety of stimuli. Beta-adrenergic stimulation and hypoxia are associated with an increase in the activity of ornithine decarboxylase, the enzyme responsible for the formation of polyamines, while aging is associated to a decrease in the activity of that enzyme. Additionally, it has been suggested that polyamines may modulate the inotropic state of the myocardium and in particular its response to Beta-adrenergic stimulation. We have attempted to define the role of polyamines on the cardiac cell function. Isolated rat ventricular myocytes were used to investigate the effect of putrescine, spermidine and spermine on the twitch and the associated cytosolic calcium transient and, in the unstimulated state, on the frequency of spontaneous calcium release from the sarcoplasmic reticulum (SR) and on resting cytosolic calcium. While putrescine had no effect on contraction and cytosolic calcium spermidine and spermine had a negative inotropic effect which was due to a decrease in the cytosolic calcium transient and not to a change in myofilament responsiveness to cytosolic calcium. In the unstimulated state there was no effect of spermine either on spontaneous SR calcium release or on resting cytosolic calcium.
