Functional difference between two isoforms of rat kidney prostaglandin receptor EP3 subtype.

We have cloned two isoforms of rat kidney prostaglandin E2 receptor EP3 subtype (rEP3A and rEP3B), which differ only in their cytosolic carboxyl-terminal tails (30 and 29 amino acids, respectively). The aim is to clarify the functional difference between two rEP3 receptor isoforms by examining formation of adenosine 3',5'-monophosphate (cAMP) and change in cytosolic free calcium ([Ca2+]i) in cultured cells transiently transfected with cloned rEP3A or rEP3B receptor cDNA. In immortalized renal distal tubule cells (TKC2), vasopressin (VP) stimulated cAMP formation, and the cAMP formation was significantly attenuated by a non-peptide VP receptor antagonist, OPC-31260. The VP-induced increase in cAMP formation was also attenuated by over-expression of rEP3A receptor but not that of rEP3B receptor. On the other hand, in COS-7 cells transfected with rEP3B receptor cDNA, PGE2 induced an increase in [Ca2+]i, but no increase in [Ca2+]i was observed in the cells transfected with rEP3A cDNA. In conclusion, rEP3A receptor is suggested to antagonize VP (V2) receptor by inhibiting cAMP formation, whereas rEP3B receptor is linked with Ca2+ messenger system.