How does acetylcholine affect heart rate of frog?

Acetylcholine (ACh) acts as a neurotransmitter in the frog's heart, primarily affecting the pacemaker cells in the sinoatrial (SA) node. When released, ACh binds to muscarinic receptors, leading to a decrease in heart rate by increasing potassium ion permeability and decreasing calcium ion influx, which slows down the depolarization phase of the action potential. This results in a more prolonged interval between heartbeats, effectively lowering the heart rate. Consequently, acetylcholine serves as a key regulator in controlling the frog's cardiac function in response to various physiological demands.