Eble D M, Qi M, Waldschmidt S, Lucchesi P A, Byron K L, Samarel A M
Cardiovascular Institute, Loyola University Chicago Stritch School of Medicine, Maywood, Illinois 60153, USA.
Am J Physiol. 1998 May;274(5):C1226-37. doi: 10.1152/ajpcell.1998.274.5.C1226.
Agonist-induced hypertrophy of cultured neonatal rat ventricular myocytes (NRVM) has been attributed to biochemical signals generated during receptor activation. However, NRVM hypertrophy can also be induced by spontaneous or electrically stimulated contractile activity in the absence of exogenous neurohormonal stimuli. Using single-cell imaging of fura 2-loaded myocytes, we found that low-density, noncontracting NRVM begin to generate intracellular Ca2+ concentration ([Ca2+]i) transients and contractile activity within minutes of exposure to the alpha 1-adrenergic agonist phenylephrine (PE; 50 microM). However, NRVM pretreated with verapamil and then stimulated with PE failed to elicit [Ca2+]i transients and beating. We therefore examined whether PE-induced [Ca2+]i transients and contractile activity were required to elicit specific aspects of the hypertrophic phenotype. PE treatment (48-72 h) increased cell size, total protein content, total protein-to-DNA ratio, and myosin heavy chain (MHC) isoenzyme content. PE also stimulated sarcomeric protein assembly and prolonged MHC half-life. However, blockade of voltage-gated L-type Ca2+ channels with verapamil, diltiazem, or nifedipine (10 microM) blocked PE-induced total protein and MHC accumulation and prevented the time-dependent assembly of myofibrillar proteins into sarcomeres. Inhibition of actin-myosin cross-bridge cycling with 2,3-butanedione monoxime (7.5 mM) also prevented PE-induced total protein and MHC accumulation, indicating that mechanical activity, rather than [Ca2+]i transients per se, was required. In contrast, blockade of [Ca2+]i transients and contractile activity did not prevent the PE-induced increase in cell surface area, activation of the mitogen-activated protein kinases ERK1 and ERK2, or upregulation of atrial natriuretic factor gene expression. Thus contractile activity is required to elicit some but not all aspects of the the hypertrophic phenotype induced by alpha 1-adrenergic receptor activation.
激动剂诱导的培养新生大鼠心室肌细胞（NRVM）肥大被归因于受体激活过程中产生的生化信号。然而，在没有外源性神经激素刺激的情况下，NRVM肥大也可由自发的或电刺激的收缩活动诱导。使用装载fura 2的肌细胞进行单细胞成像，我们发现低密度、不收缩的NRVM在暴露于α1 -肾上腺素能激动剂去氧肾上腺素（PE；50微摩尔）几分钟内就开始产生细胞内Ca2 +浓度（[Ca2 +]i）瞬变和收缩活动。然而，用维拉帕米预处理然后用PE刺激的NRVM未能引发[Ca2 +]i瞬变和搏动。因此，我们研究了PE诱导的[Ca2 +]i瞬变和收缩活动是否是引发肥大表型特定方面所必需的。PE处理（48 - 72小时）增加了细胞大小、总蛋白含量、总蛋白与DNA的比率以及肌球蛋白重链（MHC）同工酶含量。PE还刺激了肌节蛋白组装并延长了MHC半衰期。然而，用维拉帕米、地尔硫卓或硝苯地平（10微摩尔）阻断电压门控L型Ca2 +通道可阻断PE诱导的总蛋白和MHC积累，并阻止肌原纤维蛋白随时间组装成肌节。用2,3 -丁二酮单肟（7.5毫摩尔）抑制肌动蛋白 - 肌球蛋白横桥循环也可阻止PE诱导的总蛋白和MHC积累，表明需要机械活动而非[Ca2 +]i瞬变本身。相比之下，阻断[Ca2 +]i瞬变和收缩活动并不能阻止PE诱导的细胞表面积增加、丝裂原活化蛋白激酶ERK1和ERK2的激活或心房利钠因子基因表达的上调。因此，收缩活动是引发α1 -肾上腺素能受体激活诱导的肥大表型的某些而非全部方面所必需的。
