Competition studies using whole cryostat sections in the lungs from patients with PAH compared to normal control tissues did not detect a significant difference in binding affinities (KD) for ETA or ETB and no change in receptor densities (BMAX) or ratio of sub-types in human PAH lungs compared with control (Fig. 2B, Table 3). Here, EDNRB is linked to pulmonary arterial hypertension.