Henry Ford Hospital, Dept. of Medicine, Hypertension and Vascular Research Division, 7088 E&R Bldg., 2799 W. Grand Blvd., Detroit, MI 48202.
Am J Physiol Renal Physiol. 2013 Oct 15;305(8):F1209-19. doi: 10.1152/ajprenal.00710.2012. Epub 2013 Jul 24.
Renin is synthesized and released from juxtaglomerular (JG) cells. Adenosine inhibits renin release via an adenosine A1 receptor (A1R) calcium-mediated pathway. How this occurs is unknown. In cardiomyocytes, adenosine increases intracellular calcium via transient receptor potential canonical (TRPC) channels. We hypothesized that adenosine inhibits renin release via A1R activation, opening TRPC channels. However, higher concentrations of adenosine may stimulate renin release through A2R activation. Using primary cultures of isolated mouse JG cells, immunolabeling demonstrated renin and A1R in JG cells, but not A2R subtypes, although RT-PCR indicated the presence of mRNA of both A2AR and A2BR. Incubating JG cells with increasing concentrations of adenosine decreased renin release. Different concentrations of the adenosine receptor agonist N-ethylcarboxamide adenosine (NECA) did not change renin. Activating A1R with 0.5 μM N6-cyclohexyladenosine (CHA) decreased basal renin release from 0.22 ± 0.05 to 0.14 ± 0.03 μg of angiotensin I generated per milliliter of sample per hour of incubation (AngI/ml/mg prot) (P < 0.03), and higher concentrations also inhibited renin. Reducing extracellular calcium with EGTA increased renin release (0.35 ± 0.08 μg AngI/ml/mg prot; P < 0.01), and blocked renin inhibition by CHA (0.28 ± 0.06 μg AngI/ml/mg prot; P < 0. 005 vs. CHA alone). The intracellular calcium chelator BAPTA-AM increased renin release by 55%, and blocked the inhibitory effect of CHA. Repeating these experiments in JG cells from A1R knockout mice using CHA or NECA demonstrated no effect on renin release. However, RT-PCR showed mRNA from TRPC isoforms 3 and 6 in isolated JG cells. Adding the TRPC blocker SKF-96365 reversed CHA-mediated inhibition of renin release. Thus A1R activation results in a calcium-dependent inhibition of renin release via TRPC-mediated calcium entry, but A2 receptors do not regulate renin release.
肾素是由肾小球旁器（JG）细胞合成和释放的。腺苷通过腺苷 A1 受体（A1R）钙介导途径抑制肾素释放。目前尚不清楚这种情况是如何发生的。在心肌细胞中，腺苷通过瞬时受体电位经典（TRPC）通道增加细胞内钙。我们假设腺苷通过 A1R 激活，打开 TRPC 通道来抑制肾素释放。然而，较高浓度的腺苷可能通过 A2R 激活刺激肾素释放。使用分离的小鼠 JG 细胞的原代培养物，免疫标记显示 JG 细胞中存在肾素和 A1R，但不存在 A2R 亚型，尽管 RT-PCR 表明两种 A2AR 和 A2BR 的 mRNA 均存在。用递增浓度的腺苷孵育 JG 细胞可减少肾素释放。不同浓度的腺苷受体激动剂 N-乙基羧酰胺腺苷（NECA）不会改变肾素。用 0.5 μM N6-环已基腺苷（CHA）激活 A1R 可使基础肾素释放从每小时每毫克样本产生的 0.22±0.05 减少到 0.14±0.03μg 血管紧张素 I（AngI/ml/mg prot）（P<0.03），并且较高浓度也抑制肾素。用 EGTA 减少细胞外钙可增加肾素释放（0.35±0.08μg AngI/ml/mg prot；P<0.01），并阻断 CHA 对肾素的抑制作用（0.28±0.06μg AngI/ml/mg prot；P<0.005 与 CHA 单独相比）。细胞内钙螯合剂 BAPTA-AM 使肾素释放增加 55%，并阻断 CHA 的抑制作用。在 A1R 基因敲除小鼠的 JG 细胞中重复这些实验，用 CHA 或 NECA 表明对肾素释放没有影响。然而，RT-PCR 显示分离的 JG 细胞中存在 TRPC 同工型 3 和 6 的 mRNA。添加 TRPC 阻滞剂 SKF-96365 可逆转 CHA 介导的肾素释放抑制。因此，A1R 激活导致钙依赖性肾素释放抑制通过 TRPC 介导的钙内流，但 A2 受体不调节肾素释放。
