Angst B D, Khan L U, Severs N J, Whitely K, Rothery S, Thompson R P, Magee A I, Gourdie R G
Laboratory of Eukaryotic Molecular Genetics, National Institute for Medical Research, London, England.
Circ Res. 1997 Jan;80(1):88-94. doi: 10.1161/01.res.80.1.88.
Nonuniformity in the spatial patterning of gap junctions between heart muscle cells is now recognized as an important determinant of electromechanical function in working myocardium. Breakdown of the normal geometry of electrical intercellular connectivity in diseased myocardium correlates with reentry, arrhythmia, and conduction disturbance. The developmental mechanism(s) that determines this precise spatial order in gap junction organization in normal myocardium is at present unknown. To examine this question, we have used immunoelectron and immunoconfocal microscopy to analyze the spatial distributions of gap junctional (connexin43), desmosomal (desmoplakin), and adherens junctional (N-cadherin) components during maturation of rodent and canine left ventricular myocardium. In rats, a striking divergence in the distribution of gap junctions and cell adhesion junctions emerged within the first 20 days of postnatal life. It was found that although gap junctions initially demonstrated dispersed distributions across myocyte cell membranes, desmosomes and adherens junctions showed more rapid polarization toward cell termini (ie, nascent intercalated disks) after birth. Over subsequent postnatal development (20 to 90 postnatal days), gap junctions became progressively concentrated in these cell adhesion junction-rich zones of membrane. Quantitative analyses of this process in a series of rats aged 15 embryonic and 1, 5, 10, 20, 40, 70, and 90 postnatal days indicated that significantly higher levels (P < .01) of N-cadherin and desmoplakin than of connexin43 were immunolocalized to cell termini by as early as postnatal day 5. Although all three junctions types showed increasing polarization to myocyte termini with development, variation between junctions remained significant (P < .05) at all times points between 5 and 70 postnatal days. Only at 90 postnatal days, when the animals were nearly full grown, did the proportions of gap junction, desmosome, and adherens junction at intercalated disks become statistically similar (P > .05). Examination of myocardium from 1- and 3-month-old canines revealed that related differential changes to the spatiotemporal distribution of intercellular junctions occurred during postnatal maturation of the dog heart, suggesting that the process was not rodent specific. It is concluded that this progressive change in the organization and pattern of association between gap junctions and cell adhesion junctions is likely to be an important factor in maturation of electromechanical function within the mammalian heart.
心肌细胞间缝隙连接的空间分布不均一性现已被认为是工作心肌电机械功能的一个重要决定因素。患病心肌中细胞间电连接正常几何结构的破坏与折返、心律失常及传导障碍相关。目前尚不清楚在正常心肌中决定缝隙连接组织这种精确空间秩序的发育机制。为研究此问题，我们利用免疫电子显微镜和免疫共聚焦显微镜分析了啮齿动物和犬左心室心肌成熟过程中缝隙连接（连接蛋白43）、桥粒（桥粒斑蛋白）和黏着连接（N-钙黏着蛋白）成分的空间分布。在大鼠中，出生后第1个20天内缝隙连接和细胞黏附连接的分布出现显著差异。研究发现，虽然缝隙连接最初在心肌细胞膜上呈分散分布，但出生后桥粒和黏着连接向细胞末端（即新生闰盘）的极化更快。在出生后的后续发育阶段（出生后20至90天），缝隙连接逐渐集中在这些富含细胞黏附连接的膜区。对一系列年龄为胚胎期15天及出生后1、5、10、20、40、70和90天的大鼠进行的这一过程的定量分析表明，早在出生后第5天，N-钙黏着蛋白和桥粒斑蛋白免疫定位到细胞末端的水平就显著高于连接蛋白43（P <.01）。尽管随着发育所有三种连接类型向心肌细胞末端的极化都增加，但在出生后5至70天的所有时间点，连接类型之间的差异仍然显著（P <.05）。仅在出生后90天，即动物几乎完全长大时，闰盘处缝隙连接、桥粒和黏着连接的比例才在统计学上变得相似（P >.05）。对1月龄和3月龄犬心肌的检查显示，犬心脏出生后成熟过程中细胞间连接的时空分布发生了相关的差异变化，表明该过程并非啮齿动物所特有。得出的结论是，缝隙连接与细胞黏附连接之间组织和关联模式的这种渐进变化可能是哺乳动物心脏电机械功能成熟的一个重要因素。
