Wong N L, Tsui J K
Department of Medicine, University of British Colombia, Vancouver, British Columbia, Canada.
Metabolism. 2001 Jun;50(6):661-6. doi: 10.1053/meta.2001.23293.
Our recent studies showed that endothelin (ET)(B) receptors are downregulated in congestive heart failure. These changes in ET(B) receptor density can be prevented by angiotensin-converting enzyme inhibitors, suggesting a possible role for angiotensin. Using isolated inner medullary collecting ducts (IMCD), we examined the possibility that angiotensin-induced downregulation of ET(B) receptors is accompanied by a decrease in ET(B) receptor mRNA. Binding studies showed that overnight incubation with angiotensin II induced a downregulatiion of ET(A) and ET(B) receptors' density in IMCD by 39% and 29%, respectively. This downregulation in ET receptor density was abolished when IMCD was coincubated with angiotensin II and its receptor antagonist saralasin. Furthermore, when the cells were exposed to phorbol myristate acetate (PMA), it resulted in a reduction in ET(A) and ET(B) receptor binding sites by 41% and 34%, respectively, suggesting the involvement of protein kinase C (PKC). In isolated IMCD, ET-1 induced an increase in cyclic guanosine monophosphate (cGMP) accumulation (705 + 63 to 1,015 + 88 fmol/microg protein/5min, P <.01), and the ET-1-induced accumulation was attenuated in the presence of angiotensin II (641 + 45 to 809 + 46 fmol/microg protein/5min, P <.01). Using competitive polymerase chain reaction (PCR) method, we also observed downregulation of ET(A) and ET(B) receptors mRNA in IMCD treated with angiotensin II (ET(A), 1.09+0.11 v 0.77 + 0.07 amol/microg of total RNA, P <.01; ET(B), 14.80 + 1.95 v 8.65 + 0.67 amol/microg of total RNA, P <.01). The addition of a PKC inhibitor abolished the downregulation of ET(A) and ET(B) receptor mRNA induced by angiotensin II (ET(A), 1.25 + 0.07 v 1.19 + 0.06 amol/microg of total RNA, not significant [NS]; ET(B), 14.36 + 0.83 to 13.68 + 0.64 amol/microg of total RNA, NS). These results suggest that angiotensin II-induced downregulation of ET(A) and ET(B) receptors mRNA is mediated by a mechanism involving PKC.
我们最近的研究表明，在充血性心力衰竭中内皮素（ET）（B）受体下调。ET（B）受体密度的这些变化可被血管紧张素转换酶抑制剂阻止，提示血管紧张素可能发挥作用。利用分离的肾内髓集合管（IMCD），我们研究了血管紧张素诱导的ET（B）受体下调是否伴有ET（B）受体mRNA减少的可能性。结合研究显示，与血管紧张素II过夜孵育分别导致IMCD中ET（A）和ET（B）受体密度下调39%和29%。当IMCD与血管紧张素II及其受体拮抗剂沙拉新共同孵育时，ET受体密度的这种下调被消除。此外，当细胞暴露于佛波酯肉豆蔻酸酯（PMA）时，ET（A）和ET（B）受体结合位点分别减少41%和34%，提示蛋白激酶C（PKC）参与其中。在分离的IMCD中，ET-1诱导环磷酸鸟苷（cGMP）积累增加（从705 + 63至1,015 + 88 fmol/μg蛋白/5分钟，P <.01），并且在血管紧张素II存在时ET-1诱导的积累减弱（从641 + 45至809 + 46 fmol/μg蛋白/5分钟，P <.01）。使用竞争性聚合酶链反应（PCR）方法，我们还观察到用血管紧张素II处理的IMCD中ET（A）和ET（B）受体mRNA下调（ET（A），1.09 + 0.11对0.77 + 0.07 amol/μg总RNA，P <.01；ET（B），14.80 + 1.95对8.65 + 0.67 amol/μg总RNA，P <.01）。添加PKC抑制剂消除了血管紧张素II诱导的ET（A）和ET（B）受体mRNA下调（ET（A），1.25 + 0.07对1.19 + 0.06 amol/μg总RNA，无显著差异[NS]；ET（B），14.36 + 0.83至13.68 + 0.64 amol/μg总RNA，NS）。这些结果表明血管紧张素II诱导的ET（A）和ET（B）受体mRNA下调是由涉及PKC的机制介导的。
