Negative chronotropic effect of dibutyryl cyclic AMP on the cultured chick embryonic heart cells and the prolongation of the action potential duration.

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Abstract
There were clear differences between the effects of norepinephrine and dibutyryl cAMP on the cultured chick embryonic heart cells. Norepinephrine and dibutyryl cAMP were applied to the cultured chick embryonic heart cells and the changes in the beating rate and the action potential configuration were examined. Norepinephrine increased the beating rate, but dibutyryl cAMP produced the significant negative chronotropic effect. Norepinephrine increased the slope of the diastolic depolarization with little affecting the duration of the action potential. Dibutyryl cAMP significantly prolonged the action potential duration without changing the slope of the diastolic depolarization. Dibutyryl cAMP did not always produce the positive chronotropism and the negative chronotropism on the cultured chick embryonic heart cells may be related to the prolongation of the action potential duration.