FUNCTIONAL-PROPERTIES OF HIGH-AFFINITY AND LOW-AFFINITY RECEPTOR SUBTYPES FOR ENDOTHELIN-3

Endothelial cells from brain microvessels express two types of endothelin (ET) receptor. The first receptor subtype (defined as E-alpha) shows a high affinity for ET-1, a low affinity for ET-3, and it is coupled to phospholipase C. The second subtype (E-beta) shows a high affinity for both ET-1 and ET-3. It is not coupled to phospholipase C, but its activation leads to an increased activity of the Na+/H+ exchanger via a protein kinase C-independent mechanism. Brain astrocytes also express a high-affinity ET-3 receptor. However, unlike that of brain capillary endothelial cells, this receptor is coupled to phospholipase C and it may be a third type of endothelin receptor (E-gamma). Thus, it seems that by using both binding and functional criteria, at least three subtypes of endothelin receptor can be distinguished: a low-affinity ET-3 receptor and two high-affinity ET-3 receptors that are coupled to different intracellular signaling pathways.