How do cholinergic agents affect heart rate?

Cholinergic agents primarily act by stimulating the parasympathetic nervous system, which uses the neurotransmitter acetylcholine. The activation of muscarinic receptors, particularly in the heart, leads to a reduction in heart rate, a phenomenon known as negative chronotropic effect. When acetylcholine binds to these receptors, it enhances the activity of potassium channels, causing hyperpolarization of the pacemaker cells in the sinoatrial node, thus decreasing the rate of depolarization and subsequently reducing heart rate.

In contrast, other choices do not align with the essential understanding of cholinergic pharmacodynamics. While dosages can impact how pronounced the effects are, the fundamental action of cholinergic agents on heart rate is to lower it. They typically do not increase heart rate and are not known for having no effect. Overall, the predominant response of these agents on heart rate is a decrease, making this the correct characterization of their action.