Iontrophoretic application of autonomic mediators and cyclic nucleotides in the sinus node cells.

The effects of intracellular application of noradrenaline, acetylcholine, cAMP and cGMP were studied in the sinus-node of the rabbit. Noradrenaline and acetylcholine were without effect on electrical activity. In about one third of cases, cAMP increased, and cGMP decreased the slope of slow depolarization. These results suggest that adrenergic as well as cholinergic receptors which control the electrical activity of the sinus node cell are localized at the outer side of the cell membrane. It has also been shown that the cyclic nucleotides exert direct but opposite chronotropic effects.