Acetylcholine-norepinephrine interactions on potassium movements in the sinus node.

Possible adrenergic mechanisms involved in acetylcholine (ACh) induced potassium movements in the sinus node have been investigated using a tracer potassium (42K) and a microelectrode technique. The ACh-induced increase in 42K uptake was enhanced by propranolol and was unaffected by phentolamine. Reserpinization neither prevented the ACh-induced increase in 42K uptake nor the enhanced effect in the presence of propranolol. In reserpinized preparations, ACh-induced 42K uptake was the same before and after norepinephrine (NE) administration, but was greater after acute reserpinization. NE alone induced an increase in 42K uptake but the simultaneous administration of ACh and NE provoked an increase in 42K uptake similar to that obtained with ACh alone. When both neuromediators and atropine were given simultaneously, an increase in 42K uptake did not occur. Thus, the ACh induces an increase in 42K uptake independently of NE. ACh antagonizes the NE effect on 42K uptake independently of a muscarinic interaction.