Transcription of dopamine D1A receptor mRNAs in rat heart

The existence of dopamine receptor subtypes in the heart has been suggested by pharmacological and biochemical techniques. So far, however, very little data is available as to the transcription of dopamine D1 subtype receptor genes in the heart. Therefore, in this study we employed reverse transcription-polymerase chain reaction (RT-PCR), which is a sensitive and highly specific method for identifying a low abundance mRNA in tissues, to determine if the D1A receptor gene was transcripted in the adult rat heart. Total RNA was isolated from the whole heart by the guanidium thiocyanate-CsCl method. Primers were based on the sequence of rat D1A cDNA cloned from the brain and corresponded to the third cytoplasmic loop of the receptor. A predicted size product (247bp) was evident from heart RNA. PCR performed in the absence of reverse transcriptase did not result in an amplification of the predicted product, indicating that these products were from cDNA and not from genomic DNA. The results demonstrate the existence of D1A receptor mRNA in the rat heart and that the D1A receptor in the heart are possibly identical to that from the brain. Since in this study the whole heart RNA was used, we cannot ascertain whether the mRNA comes from cardiac myocyte per se or from intermuscular coronary arterioles or from both.