Characterization of a rat kidney thromboxane A2 receptor: high affinity for the agonist ligand I-BOP

We have cloned a rat kidney thromboxane A2 receptor (TP) cDNA. This receptor was shown to be functional in that the thromboxane A2 mimetics, U46619 and I-BOP, elicited calcium transients in Xenopus oocytes and HEK293 cells expressing the TP receptor, respectively. Comparison of the affinities of the rat and human TP sites for the agonist radiolgand [125 I] BOP showed that the rat TP site has about a ten-fold higher affinity for this drug (KD approximately 0.5 vs. 4.4 nM) while the affinities of the two sites for other compounds (U46619, I-PTH-OH) were the same. Our results are significant in that they identify a cloned TP as having a picomolar affinity for [125 I] BOP.