Subtype-specific desensitization of human endothelin ETA and ETB receptors reflects differential receptor phosphorylation.
Endothelins regulate blood pressure in mammals through G protein-coupled receptors. Two receptor subtypes, ETA and ETB, exist which differ by their agonist profiles. Here we show subtype-specific differences in the inactivation of these endothelin receptors. Using a modified inositol phosphate accumulation assay, we found that stimulation of ETA by endothelin-1 results in sustained activation of the subtype, retaining >30% of its initial activity even 20 min after agonist administration, whereas the ETB rapidly deactivated after agonist stimulation, losing >80% of its initial activity within 5 min after endothelin application. The discrepancy in receptor inactivation is reflected by subtype-specific differences in receptor phosphorylation. Whereas ETA failed to undergo ligand-induced phosphorylation, the ETB was rapidly phosphorylated in response to agonist stimulation. By contrast, the kinetics of ligand-induced internalization were essentially identical for the receptor subtypes, suggesting endothelin receptor internalization being independent of ligand-induced receptor phosphorylation. Interestingly, a strong correlation was observed between the time course of ETA inactivation and ETA internalization. Therefore, our data suggest a subtype-specific inactivation of human endothelin receptors: fast receptor phosphorylation in the case of ETB and slow receptor internalization in the case of ETA. Subtype-specific modulation of endothelin receptors may account for the short-term hypotensive effects of endothelins via rapidly down-regulating ETB receptors and the long-lasting hypertensive effects due to sustained ETA activation.
Cramer
H
H
Institute for Physiological Chemistry and Pathobiochemistry, University of Mainz, D-55099 Mainz, Duesbergweg 6, Germany.
Müller-Esterl
W
W
Schroeder
C
C
D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D006801:Humans; D007106:Immune Sera / Q000096:biosynthesis / Q000737:chemistry; D007700:Kinetics; D008024:Ligands; D010169:Palmitic Acids / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000502:physiology; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D017466:Receptors, Endothelin / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D018411:Spodoptera / Q000235:genetics
D007106:Immune Sera; D008024:Ligands; D010169:Palmitic Acids; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D017466:Receptors, Endothelin; D011493:Protein Kinase C