Vannier C, Veksler V, Mekhfi H, Mateo P, Ventura-Clapier R
INSERM, Université Paris-Sud, Châtenay-Malabry, France.
Can J Physiol Pharmacol. 1996 Jan;74(1):23-31.
To understand the factors underlying the functional differences between atrial and ventricular tissues, intrinsic properties of myofibrils and mitochondria of atrial skinned fibers were compared with those of fibers from adult or immature (1 and 2 weeks old) ventricular muscle. Isometric mechanical parameters were determined at various calcium concentrations in fibers treated with Triton X-100 to solubilize all cellular membranes. Maximal active tension and stiffness measured at pCa 4.5, as well as calcium sensitivity, were not different in adult atria and ventricles. Both force and stiffness increased in adult ventricles, while calcium sensitivity diminished in adult ventricles, compared with immature muscles. Myofibrillar contractile kinetics, assessed by the rate constant of tension fall following quick stretches, were similar in adult atria (79.7 +/- 6.9 s-1) and ventricles (72.4 +/- 6.8 s-1) and higher in adult atria and ventricles than in immature ventricles (24.1 +/- 2.3 s-1 in 1-week-old rats and 49.3 +/- 4.2 s-1 in 2-week-old rats). Sensitivity of rigor tension development to MgATP in the presence and in the absence of phosphocreatine was not markedly different in the different tissues. Mitochondrial function was assessed in saponin-skinned fibers. Tissue oxidative capacities, expressed as nmol O2.min-1.mg-1 fiber dry weight, were lower in immature ventricles and atria than in adult ventricles. Creatine failed to stimulate respiration in ventricles of young rats and in adult atria, whereas a 74 +/- 10% increase in respiration was observed in adult ventricles. Since mitochondrial creatine kinase was present in adult atria, this suggests an absence of coupling between oxidative phosphorylation and mitochondrial creatine kinase in this tissue. Thus, adult atrial tissue differs from neonatal ventricular tissue but it exhibits contractile properties similar to adult ventricular properties and differs from adult ventricle mainly in metabolic properties.
为了解心房和心室组织功能差异的潜在因素，将心房剥除肌纤维的肌原纤维和线粒体的内在特性与成年或未成熟（1周和2周龄）心室肌纤维的特性进行了比较。在用 Triton X - 100处理以溶解所有细胞膜的纤维中，在不同钙浓度下测定等长力学参数。在pCa 4.5时测得的最大主动张力和刚度以及钙敏感性，在成年心房和心室中并无差异。与未成熟肌肉相比，成年心室的力量和刚度均增加，而钙敏感性降低。通过快速拉伸后张力下降的速率常数评估的肌原纤维收缩动力学，在成年心房（79.7±6.9 s⁻¹）和心室（72.4±6.8 s⁻¹）中相似，且成年心房和心室中的收缩动力学高于未成熟心室（1周龄大鼠为24.1±2.3 s⁻¹，2周龄大鼠为49.3±4.2 s⁻¹）。在有无磷酸肌酸的情况下，不同组织中强直张力发展对MgATP 的敏感性并无明显差异。在皂角苷处理的剥除肌纤维中评估线粒体功能。以nmol O₂·min⁻¹·mg⁻¹纤维干重表示的组织氧化能力，在未成熟心室和心房中低于成年心室。肌酸未能刺激幼鼠心室和成年心房的呼吸，而在成年心室中观察到呼吸增加了74±10%。由于成年心房中存在线粒体肌酸激酶，这表明该组织中氧化磷酸化与线粒体肌酸激酶之间不存在偶联。因此，成年心房组织不同于新生心室组织，但它表现出与成年心室相似的收缩特性，主要在代谢特性上与成年心室不同。
