Atropine and Its Derivatives

The antimuscarinic drug atropine, and its derivative ipratropiumbromide, can also be used for antiarrhyth-mic treatment. Muscarinic receptors (M2 subtype) are mainly present in supraventricular tissue and in the AV node. They inhibit adenylylcyclase via G proteins and thereby reduce intracellular cAMP. On the other hand, activation of the M2 receptor leads to opening of hyperpolarizing Ik.acii and inhibits the pacemaker current If probably via the (3y-subunit of the Gi protein associated with this receptor. The results are hyperpolarization and slower spontaneous depolarization. Muscarinic receptor antagonists like atropine lead to increased heart rate and accelerated atrioventricular conduction. There are no or only slight effects on the ventricular electrophysiology. 

Anticholinergics, like atropine and its derivative ipratropium bromide block cholinergic pathways that cause airway constriction. They may provide added bronchodi-lator effect in patients who are receiving beta -adrenergic agents for asthma. 

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