The prostaglandin EP4 receptor is a relaxant prostanoid receptor that becomes insensitive after being activated due to homologous desensitization and, in some cases, to heterologous desensitization.
EP4 is classified as a relaxant type of prostaglandin receptor based on its ability, upon activation, to relax the contraction of certain smooth muscle preparations and smooth muscle-containing tissues that have been pre-contracted by stimulation. Following its activation, EP4 undergoes homologous desensitization. That is, EP4 becomes insensitive to further activation and internalizes. Agents which activate certain isoforms of protein kinase C can also desensitize EP4 by a process termed heterologous desensitization. 
