G protein-coupled receptor for 5-hydroxytryptamine (serotonin), a biogenic hormone that functions as a neurotransmitter, a hormone and a mitogen (PubMed:10821780, PubMed:16102731, PubMed:35714614, PubMed:9603189). Ligand binding causes a conformation change that triggers signaling via guanine nucleotide-binding proteins (G proteins) and modulates the activity of downstream effectors (PubMed:16102731, PubMed:35714614). HTR4 is coupled to G(s) G alpha proteins and mediates activation of adenylate cyclase activity (PubMed:16102731, PubMed:35714614). {ECO:0000269|PubMed:10821780, ECO:0000269|PubMed:16102731, ECO:0000269|PubMed:35714614, ECO:0000269|PubMed:9603189}. This is the function of ENSG00000164270 (HTR4, 5-hydroxytryptamine receptor 4).