Figure 9.

Schematic diagram of the location and function of ET_A and ET_B receptors in 3 tissue assays. (A) ET_A receptors located on vascular smooth muscle mediate contraction. ET_A receptors are internalized and recycled slowly through endosomes.36 (B) ET_B receptors located on smooth muscle cells mediate contraction and are rapidly removed by phosphorylation.36 (C) ET_B receptors located on smooth muscle cells bind endothelin‐1 and clear endothelin‐1 from the environment through lysosomal metabolism. The remaining endothelin‐1 binds to ET_A and ET_B receptors on smooth muscle to mediate contraction before being recycled by endosomes or destroyed by phosphorylation, respectively. In (A) and (C), ET_B receptors on the endothelium mediate release of NO that transiently relaxes smooth muscle. Examples of the species and tissues assumed to have these particular receptor profiles are given below each panel. ET‐1, endothelin‐1. NO, nitric oxide