Abstract
It was shown that there were clear differences between the effects of norepinephrine and dibutyryl cyclic AMP on the cultured chick embryonic heart cells. Norepinephrine and dibutyryl cyclic AMP 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 cyclic AMP produced the significant negative chronotropic effect. Norepinephrine increased the slope of the diastolic depolarization with little affecting the duration of the action potential. In contrast, dibutyryl cyclic AMP significantly prolonged the action potential duration without changing the slope of the diastolic depolarization. Thus, it was shown that dibutyryl cyclic AMP did not always produce the positive chronotropism, and it was suggested that the negative chronotropism on the cultured chick embryonic heart cells was related to the prolongation of the action potential duration.
