G Protein-Coupled Receptors: Gq, Gs, and Gi Pathways Explained

📝 Free GPCR Signaling Cheat Sheet: https://thecrnaclub.com/free/gpcr-sig... 🎓 Try The CRNA Club free for 7 days: https://thecrnaclub.com G protein-coupled receptors (GPCRs) sit in the cell membrane and pass a drug, hormone, or neurotransmitter signal to a G protein inside the cell. Gq-coupled receptors activate phospholipase C, and IP3 releases stored calcium. Gs-coupled receptors raise cyclic AMP and activate PKA. Gi-coupled receptors lower cyclic AMP, and their beta-gamma pair opens potassium channels. Phenylephrine tightens blood vessels, albuterol opens the airway, and Precedex turns down the sympathetic nervous system. All three send their message through G protein-coupled receptors. Sachi, a practicing CRNA and founder of The CRNA Club, starts with what a receptor is, compares the four major receptor families, and defines every part of the G-protein relay before following Gq, Gs, and Gi signaling to the effects you see at the bedside. You'll learn why calcium doesn't always mean contraction, why beta-1 and beta-2 both use Gs and still act differently in heart muscle and airway smooth muscle, how milrinone raises cyclic AMP by blocking phosphodiesterase 3 instead of activating a receptor, and how to walk through a drug's mechanism step by step in a CRNA school interview. Inside The CRNA Club you'll find more than 200 videos in the Learning Library, CCRN and CMC review courses with quiz banks, the AI Mock Interview Lab, the School Database, the Transcript Analyzer, and resume and essay smart tools. In this video: 0:00 Why do 3 different drugs share 1 receptor family? 0:55 What is a receptor? 1:36 What are the 4 major receptor families? 3:25 How does a G protein-coupled receptor work? 3:55 What does the G protein do? 4:48 What do Gq-coupled, Gs-coupled, and Gi-coupled mean? 5:28 What is a second messenger? 5:54 How does the Gq pathway work? 7:02 Does calcium always mean contraction? 8:02 Which bedside drugs use the Gq pathway? 8:53 How does the Gs pathway work? 9:35 How does beta-1 make the heart contract harder? 10:56 How does albuterol relax the airway through beta-2? 11:38 Why does epinephrine act differently in each tissue? 11:53 How does milrinone raise cyclic AMP? 12:39 How are Gq and Gs different? 12:51 How does the Gi pathway work? 14:11 What does Gi do in the heart and brain? 14:59 Why does Precedex cause bradycardia and a low MAP? 16:13 How do you explain a drug in a CRNA school interview? 16:59 How do Gq, Gs, and Gi compare? FAQ: Q: What is the difference between Gq, Gs, and Gi? A: Gq, Gs, and Gi name the alpha-subunit family of the G protein a receptor activates. Gq activates phospholipase C and raises calcium inside the cell. Gs stimulates adenylyl cyclase and raises cyclic AMP. Gi inhibits adenylyl cyclase, lowers cyclic AMP, and its beta-gamma pair opens potassium channels. Q: Which receptors are Gq-coupled? A: Alpha-1 adrenergic, vasopressin V1a, and muscarinic M3 receptors are three Gq-coupled examples ICU nurses see often. Phenylephrine on alpha-1 receptors releases stored calcium in vascular smooth muscle, which activates myosin light-chain kinase and constricts the vessel. Q: Is milrinone a beta agonist? A: No. Milrinone blocks phosphodiesterase 3 (PDE3), so cyclic AMP breaks down more slowly. Beta-1 signaling makes more cyclic AMP, and milrinone keeps it around longer. That supports stronger heart contraction and relaxes vascular smooth muscle, which is why milrinone is called an inodilator. Sources: IUPHAR/BPS Guide to Pharmacology: https://www.guidetopharmacology.org/ Concise Guide to Pharmacology 2025/26: https://discovery.ucl.ac.uk/id/eprint... NCBI Bookshelf, Adrenergic Drugs: https://www.ncbi.nlm.nih.gov/books/NB... NCBI Bookshelf, Receptor Types: https://www.ncbi.nlm.nih.gov/books/NB... NCBI Bookshelf, G-Protein-Linked Cell-Surface Receptors: https://www.ncbi.nlm.nih.gov/books/NB... NCBI Bookshelf, Intracellular Signal Transduction: https://www.ncbi.nlm.nih.gov/books/NB... NCBI Bookshelf, Vascular Smooth Muscle Structure and Function: https://www.ncbi.nlm.nih.gov/books/NB... NCBI Bookshelf, Milrinone: https://www.ncbi.nlm.nih.gov/books/NB... Follow The CRNA Club: 🎙️ Podcast: https://podcasts.apple.com/us/podcast... | https://open.spotify.com/show/0gUh0tk... 📸 Instagram:   / thecrnaclub   🌐 Website: https://thecrnaclub.com Tags: G protein-coupled receptors, GPCR, Gq Gs Gi, Gq pathway, Gs pathway, Gi pathway, second messenger, cyclic AMP, pharmacology for nurses, ICU nurse pharmacology, CRNA school, milrinone mechanism