Ruskoaho H, Vuolteenaho O, Leppäluoto J
Department of Pharmacology and Toxicology, University of Oulu, Finland.
Endocrinology. 1990 Nov;127(5):2445-55. doi: 10.1210/endo-127-5-2445.
Stretching of atrial myocytes stimulates atrial natriuretic peptide (ANP) secretion, but the cellular processes linking mechanical distention to ANP release are unknown. We studied whether or not protein kinase C activation by phorbol ester affects atrial stretch-induced ANP secretion using the modified perfused rat heart preparation that enabled stepwise distention of the right atrium as an experimental model for stretch-stimulated ANP release. The increase in right atrial pressure (2.65 +/- 0.13 mm Hg) was accompanied by an increase in the perfusate immunoreactive ANP (IR-ANP) concentration (from 8.3 +/- 1.1 ng/5 min to 13.9 +/- 2.0 ng/5 min, P less than 0.05, n = 14). During stretch, a slight inotropic response was observed, while heart rate and perfusion pressure remained unchanged. Increase in right atrial pressure in the presence of a phorbol ester, 12-O-tetradecanoyl-phorbol-13-acetate (TPA), known to stimulate protein kinase C activity in heart cells, resulted in a significantly greater increase in the perfusate IR-ANP concentration than after vehicle infusion. The calculated ANP increase corresponding to the 2 mm Hg increase in the right atrial pressure was 1.52-fold in the control group and 1.84-fold when 10 nM TPA was infused (P less than 0.05). Infusion of TPA at a dose of 24 nM further increased the stretch-induced ANP release by causing 2.22-fold (P less than 0.01) increase in IR-ANP secretion. As judged by gel filtration chromatography, abnormal release of the large mol wt stored ANP could not account for the secretory response to phorbol ester. Additionally, a phorbol ester analog, 4 alpha-phorbol 12,13-didecanoate, which is incapable of binding to and activating protein kinase C, was inactive as an ANP secretagogue. In contrast, drugs known to increase the concentration of intracellular Ca2+ in myocytes, Bay K8644 (3 and 6 microns) and forskolin (0.14 microM), significantly inhibited the stretch-stimulated ANP release. This study shows that phorbol ester enhances atrial stretch-stimulated ANP secretion from the isolated perfused heart, suggesting that protein kinase C activity is positively coupled to the stretch-induced ANP release. The results further demonstrate the negative effect of increase in intracellular Ca2+ on stretch-induced ANP release.
心房肌细胞的拉伸可刺激心房利钠肽（ANP）分泌，但将机械牵张与ANP释放联系起来的细胞过程尚不清楚。我们使用改良的灌注大鼠心脏标本，将右心房逐步扩张作为牵张刺激ANP释放的实验模型，研究佛波酯激活蛋白激酶C是否会影响心房牵张诱导的ANP分泌。右心房压力升高（2.65±0.13毫米汞柱）伴随着灌注液中免疫反应性ANP（IR-ANP）浓度升高（从8.3±1.1纳克/5分钟升至13.9±2.0纳克/5分钟，P<0.05，n = 14）。在牵张过程中，观察到轻微的正性肌力反应，而心率和灌注压力保持不变。在已知可刺激心脏细胞中蛋白激酶C活性的佛波酯12-O-十四酰佛波醇-13-乙酸酯（TPA）存在的情况下，右心房压力升高导致灌注液中IR-ANP浓度的升高显著大于输注溶剂后的升高。对应于右心房压力升高2毫米汞柱，对照组中计算出的ANP升高为1.52倍，输注10纳摩尔TPA时为1.84倍（P<0.05）。以24纳摩尔的剂量输注TPA通过使IR-ANP分泌增加2.22倍（P<0.01）进一步增加了牵张诱导的ANP释放。通过凝胶过滤色谱判断，大分子质量储存型ANP的异常释放不能解释对佛波酯的分泌反应。此外，一种不能结合并激活蛋白激酶C的佛波酯类似物4α-佛波醇12,13-十二烷酸酯作为ANP促分泌剂无活性。相反，已知可增加心肌细胞内Ca2+浓度的药物，如Bay K8644（3和6微摩尔）和福斯可林（0.14微摩尔），显著抑制牵张刺激的ANP释放。本研究表明，佛波酯可增强离体灌注心脏中牵张刺激的ANP分泌，提示蛋白激酶C活性与牵张诱导的ANP释放呈正相关。结果进一步证明细胞内Ca2+升高对牵张诱导的ANP释放具有负性作用。
