Inwardly rectifying K⁺ channels (Kir3.1/3.2) are the primary downstream effectors of Gi-coupled receptors including opioid (μ, δ), dopamine D2, 5-HT1A, GABA-B, A1 adenosine, and muscarinic M2 receptors. GIRK mediates vagal heart rate slowing in the sinoatrial node. In DRG neurons, GIRK channels mediate the hyperpolarizing component of opioid analgesia.