Fig. 5. RT-PCR analysis of ET_A and ET_B mRNAs in heart tubes during organ culture. (A) Amplification of ET_A (top) and ET_B (bottom) cDNA from heart tubes just after isolation with various cycles of PCR. The number of cycles are indicated. m, molecular weight marker. (B) RT-PCR analysis of ET_A and ET_B expression during organ culture. The number of days in culture are indicated. GAPDH served as internal control to normalize the data. RT+, RT-PCR with reverse transcriptase. RT-, RT-PCR without reverse transcriptase. (C) Changes in ET_A and ET_B expression during organ culture. RT-PCR signals of ET receptors (I_ETR) and GAPDH (I_GAPDH) were normalized by an expected degree of PCR amplification, 2^m and 2ⁿ, respectively. The data are presented as a ratio of ET receptor signal to GAPDH signal from three independent analyses. Bars indicate standard deviation.