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

Abstract

1 We con®rmed 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. 2 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 mM), an ET A R antagonist. 3 Pretreatment with 1 nM sarafotoxin S6c (S6c), an ET B R agonist, desensitized the ET B2 R and signi®cantly attenuated the response to ET-3 (pD 2 =7.40+0.02 before, 56.50 after S6c). 4 Pretreatment with S6c had little e ect on the response to ET-1, but BQ123 (10 mM) 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). 5 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). 6 Competitive displacement experiments using membranes from late passage VSMC con®rmed only the presence of the ET A R (ET-1 pIC 50 =9.3, BQ123 pIC 50 =8.0, S6c pIC 50 56.0). 7 The ET A R was functionally active and coupled to rises in intracellular calcium which exhibited prolonged homologous desensitization. 8 Using a reverse transcriptase polymerase chain reaction for the rabbit ET B2 R, we demonstrated the absence of mRNA expression in phenotypically modi®ed VSMC. 9 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.

Pressure-Induced Upregulation of Preproendothelin-1 and Endothelin B Receptor Expression in Rabbit Jugular Vein In Situ

“…However, when the segments were pressurized for 3 hours (ie, when the pressure-induced increase in prepro-ET-1 mRNA abundance was still rather small; see Figure 4a), the potentiation of the constrictor response to S6c was comparable to that of S6b after 6 hours exposure to 20 mm Hg. Therefore, it may be that the ET B -R is rapidly desensitized by endogenous ET-1 25 and that this desensitization (or shift in affinity) can be overcome by S6b but not S6c. Notwithstanding these considerations, the superfusion bioassay data demonstrate that the pressure-induced increase in ET B -R mRNA abundance in the isolated perfused rabbit jugular vein is accompanied by an increase in functional ET B -R protein.…”

Localization and function of ET‐1 and ET receptors in small arteries post‐myocardial infarction: Upregulation of smooth muscle ETB receptors that modulate contraction

“…ET A receptor expression is reported to be decreased post‐MI in mesenteric arteries ( Fu et al ., 1993 ). These effects might be associated with a phenotypic change of vascular smooth muscle cells in disease ( Adner et al ., 1998 ; Eguchi et al ., 1994 ; Owe‐Young et al ., 1999 ), or they might occur under the influence of angiotensin II ( Kanno et al ., 1993 ) or ET‐1 itself ( Hamilton et al ., 1994 ; Hirata et al ., 1988 ). Circulating levels of ET‐1 and its big ET‐1 precursor are increased in a range of cardiovascular diseases, due to increased synthesis or reduced clearance ( Haynes & Webb, 1998 ).…”

Regional modulation of cyclic nucleotides by endothelin‐1 in rat pulmonary arteries: direct activation of Gi2‐protein in the main pulmonary artery

“…In studying the signal transduction pathways of ET‐1 in the pulmonary artery, with an aim of correlating this with previously observed functional effects, it is preferable to use intact arteries rather than primary cultures where phenotypic changes occur, especially with respect to the ET receptor (Owe‐Young et al ., 1999). For this reason we employed homogenates from the main pulmonary arteries and the small muscular pulmonary arteries used in our previous functional studies (MacLean et al ., 1994).…”