[The effect of trifluoroperazine on cAMP levels in the rat myocardium during various phases of heart cycle].

Trifluoperazine, a calmodulin inhibitor, has been studied for its effect on cAMP content in rat heart tissue at various cardiac cycle stages with beta-adrenoreceptors stimulation by izadrine. When trifluoperazine is absent, the cAMP level is found to be decreased at the beginning of the cardiac cycle in comparison with the middle of the cardiac cycle. Trifluoperazine (6 X 10(-6) M) induces an increase of the content of cyclic nucleotides at the beginning of the cardiac cycle and has no effect on its level in the middle of the cardiac cycle. This leads to a decrease of the difference between cAMP concentrations in the defined cardiac cycle regions. The calmodulin-dependent reactions might be expected to play an important role in the regulation of the myocardium cAMP concentration change during the cardiac cycle.