Differential cholinergic sensitivity of sinus and AV nodes.

The effects of the muscarinic antagonist gallamine were studied in anesthetized dogs via selective perfusion of the SA and AV nodal arteries. Before gallamine, acetylcholine injected into the SA node artery induced asystole while injection into the AV node artery induced heart block. After gallamine, acetylcholine via the AV node artery was without effect while, via the SA node artery, acetylcholine still induced negative chronotropic effects. Thus the muscarinic receptors of the SA and AV nodes may be inhomogeneous.