Schorb W, Booz G W, Dostal D E, Conrad K M, Chang K C, Baker K M
Weis Center for Research, Geisinger Clinic, Danville, Pa 17822.
Circ Res. 1993 Jun;72(6):1245-54. doi: 10.1161/01.res.72.6.1245.
Angiotensin II has been reported to be a hormonal stimulus of cardiac growth, a response that may involve myocyte hypertrophy as well as growth of nonmyocytes. This study was designed to determine whether neonatal rat cardiac fibroblasts have an angiotensin II receptor that is coupled with hypertrophic and/or proliferative growth. Competitive radioligand binding studies showed that cardiac fibroblasts have a single class of high-affinity (IC50, 1.0 nM) angiotensin II binding sites (Bmax, 778 fmol/mg protein) that are sensitive to the competitive nonpeptide AT1 receptor antagonist losartan (IC50, 13 nM). Other angiotensin peptides competed for [125I]angiotensin II binding in the following rank order: angiotensin II > angiotensin III > angiotensin I > > [des-Asp1-des-Arg2]angiotensin II. A nonhydrolyzable analogue of guanosine triphosphate increased the dissociation rate of bound [125I]angiotensin II and decreased hormone binding to the receptor at equilibrium. The angiotensin II receptor was coupled with increases in intracellular calcium. Incorporation of precursors into protein, DNA, and RNA in response to angiotensin II was determined. In serum-deprived cultures, a 24-hour exposure to 1 microM [Sar1]angiotensin II increased rates of phenylalanine, thymidine, and uridine incorporation by 58%, 103%, and 118%, respectively. These increases were blocked by the noncompetitive AT1 receptor antagonist EXP3174. After 48 hours, [Sar1]angiotensin II increased total protein and DNA of cardiac fibroblasts by 23% and 15%, respectively, with no change in the protein/DNA ratio. [Sar1]Angiotensin II increased cell number by 138% after a 24-hour exposure, without affecting cell area. In summary, cardiac fibroblasts have G protein-linked AT1 receptors that are coupled with proliferative growth. These results suggest that angiotensin II-induced cardiac hypertrophy is, in part, secondary to stimulated increases in nonmyocyte cellular growth.
据报道，血管紧张素II是心脏生长的一种激素刺激因子，这种反应可能涉及心肌细胞肥大以及非心肌细胞的生长。本研究旨在确定新生大鼠心脏成纤维细胞是否具有与肥大和/或增殖性生长相关的血管紧张素II受体。竞争性放射性配体结合研究表明，心脏成纤维细胞具有一类单一的高亲和力（IC50，1.0 nM）血管紧张素II结合位点（Bmax，778 fmol/mg蛋白质），这些位点对竞争性非肽AT1受体拮抗剂氯沙坦敏感（IC50，13 nM）。其他血管紧张素肽对[125I]血管紧张素II结合的竞争顺序如下：血管紧张素II > 血管紧张素III > 血管紧张素I > > [去天冬氨酸1-去精氨酸2]血管紧张素II。一种不可水解的鸟苷三磷酸类似物增加了结合的[125I]血管紧张素II的解离速率，并在平衡时降低了激素与受体的结合。血管紧张素II受体与细胞内钙的增加相关。测定了血管紧张素II刺激下前体掺入蛋白质、DNA和RNA的情况。在血清饥饿培养物中，1 microM [Sar1]血管紧张素II暴露24小时分别使苯丙氨酸、胸苷和尿苷掺入率提高了58%、103%和118%。这些增加被非竞争性AT1受体拮抗剂EXP3174阻断。48小时后，[Sar1]血管紧张素II使心脏成纤维细胞的总蛋白和DNA分别增加了23%和15%，而蛋白/DNA比值没有变化。[Sar1]血管紧张素II暴露24小时后使细胞数量增加了138%，而不影响细胞面积。总之，心脏成纤维细胞具有与增殖性生长相关的G蛋白偶联AT1受体。这些结果表明，血管紧张素II诱导的心脏肥大部分是由于非心肌细胞生长的刺激增加所致。
