Hydroxycarboxylic acid receptor 1 (HCA1) G protein-coupled receptors (GPCRs, or GPRs), such as GPR81, contain 7 transmembrane domains and transduce extracellular signals through heterotrimeric G proteins.[supplied by OMIM, Feb 2005] /target-data-sheets/gpcr/gpr81 2/12/2015 9:44:24 PM