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Transcriptional down‐regulation of the rabbit pulmonary artery endothelin B receptor during phenotypic modulation

1999; Wiley; Volume: 126; Issue: 1 Linguagem: Inglês

10.1038/sj.bjp.0702280

1476-5381

R Owe‐Young, C. G. Schyvens, Raffi Qasabian, Arthur D. Conigrave, Peter S. Macdonald, Dominic J. Williamson,

Renin-Angiotensin System Studies

We confirmed that endothelium‐independent contraction of the rabbit pulmonary artery (RPA) is mediated through both an endothelin A (ET A R) and endothelin B (ET B2 R) receptor. The response of endothelium‐denuded RPA rings to endothelin‐1 (ET‐1, pD 2 =7.84±0.03) was only partially inhibited by BQ123 (10 μ M ), an ET A R antagonist. Pretreatment with 1 n M sarafotoxin S6c (S6c), an ET B R agonist, desensitized the ET B2 R and significantly attenuated the response to ET‐3 (pD 2 =7.40±0.02 before, <6.50 after S6c). Pretreatment with S6c had little effect on the response to ET‐1, but BQ123 (10 μ M ) caused a parallel shift to the right of the residual ET A R‐mediated response to ET‐1 (pD 2 =7.84±0.03 before S6c, 7.93±0.03 after S6c, 6.81±0.05 after BQ123). Binding of radiolabelled ET‐1 to early passage cultures of RPA vascular smooth muscle cells (VSMC) displayed two patterns of competitive displacement characteristic of the ET A R (BQ123 pIC 50 =8.73±0.05) or ET B2 R (S6c pIC 50 =10.15). Competitive displacement experiments using membranes from late passage VSMC confirmed only the presence of the ET A R (ET‐1 pIC 50 =9.3, BQ123 pIC 50 =8.0, S6c pIC 50 <6.0). The ET A R was functionally active and coupled to rises in intracellular calcium which exhibited prolonged homologous desensitization. Using a reverse transcriptase polymerase chain reaction for the rabbit ET B2 R, we demonstrated the absence of mRNA expression in phenotypically modified VSMC. We conclude that the ET B2 R expressed by VSMC which mediates contraction of RPA is rapidly down‐regulated at the transcriptional level during phenotypic modulation in vitro . British Journal of Pharmacology (1999) 126 , 103–110; doi: 10.1038/sj.bjp.0702280