The work reported here is an important first step toward characterizing the smooth muscle cell TxA2 receptor. A growing literature indicates that certain members of the prostanoid family are important in stimulating smooth muscle cell proliferation in vitro. However, the relationship of the in vitro and in vivo regulation patterns has yet to be determined. In order to fully understand the role of the TxA2 receptor in regulation of RASM proliferation and hypertrophy, it will be necessary to characterize how the receptor is regulated at transcriptional and translational levels. This will require cloning and characterization of the smooth muscle TxA2 receptor, particularly since pharmacological data suggest that there may be subtypes of the TxA2 receptor. The studies presented here indicate that early passage, confluent RASMs contain relatively large numbers of this receptor and can serve as a source of mRNA for construction of a cDNA library that should contain a sequence encoding the receptor.