Functional analysis and chromosomal gene assignment of rat kidney prostaglandin EP3 receptor

We have reported two isoformes of rat prostaglandin EP3 receptor with their different carboxyl-terminal tails (rEP3A and rEP3B receptors), which are derived by alternative RNA splicing, and both receptors have been shown to be localized to renal distal tubules. In the present study, we characterized the signal transduction system of rat kidney EP3 receptors either in a renal cell line mimicking renal distal tubule cells, TKC2, or in COS-7 cells by functional expression of these receptors. We also examined the chromosomal localization of the EP3 receptor gene by fluorescence in situ hybridization (FISH). In TKC2 cells, vasopressin (AVP, 10(-7) M), prostaglandin (PG) E2 (10(-7) M), or forskolin (10(-8) M) markedly stimulated cyclic AMP formation. Overexpression of the rEP3A receptor significantly attenuated the AVP-, PGE2- or forskolin-induced cyclic AMP formation, whereas there was no change with rEP3B receptor expression. On the other hand, in COS-7 cells transfected with rEP3A receptor cDNA, PGE2 (10(-7) M) did not affect cytosolic free calcium concentration ([Ca2+]i), whereas transfection of rEP3B receptor cDNA evoked PGE2-induced increases in [Ca2+]i. Moreover, we have revealed that the rEP3 receptor gene is localized to rat chromosome 2q44-45. In conclusion, rEP3A or rEP3B receptor is suggested as a mediator of the natriuretic/diuretic action of PGE2 in renal distal tubules via a decrease in cyclic AMP formation or an increase in [Ca2+]i, respectively. Information of the gene assignment of rat EP3 receptor to rat chromosome 2q44-45 is useful for further analysis of the role of EP3 receptor in genetically hypertensive rat models.