Department of Physiology, The University of Auckland, New Zealand.
J Gen Physiol. 2009 Oct;134(4):339-50. doi: 10.1085/jgp.200910276. Epub 2009 Sep 14.
Trabeculae carneae are the smallest naturally arising collections of linearly arranged myocytes in the heart. They are the preparation of choice for studies of function of intact myocardium in vitro. In vivo, trabeculae are unique in receiving oxygen from two independent sources: the coronary circulation and the surrounding ventricular blood. Because oxygen partial pressure (PO(2)) in the coronary arterioles is identical in specimens from both ventricles, whereas that of ventricular blood is 2.5-fold higher in the left ventricle than in the right ventricle, trabeculae represent a "natural laboratory" in which to examine the influence of "extravascular" PO(2) on the extent of capillarization of myocardial tissue. We exploit this advantage to test four hypotheses. (1) In trabeculae from either ventricle, a peripheral annulus of cells is devoid of capillaries. (2) Hence, sufficiently small trabeculae from either ventricle are totally devoid of capillaries. (3) The capillary-to-myocyte ratios in specimens from either ventricle are identical to those of their respective walls. (4) Capillary-to-myocyte ratios are comparable in specimens from either ventricle, reflecting equivalent energy demands in vivo, driven by identical contractile frequencies and comparable wall stresses. We applied confocal fluorescent imaging to trabeculae in cross section, subsequently using semi-automated segmentation techniques to distinguish capillaries from myocytes. We quantified the capillary-to-myocyte ratios of trabeculae from both ventricles and compared them to those determined for the ventricular free walls and septum. Quantitative interpretation was furthered by mathematical modeling, using both the classical solution to the diffusion equation for elliptical cross sections, and a novel approach applicable to cross sections of arbitrary shape containing arbitrary disposition of capillaries and non-respiring collagen cords.
心肌小梁是心脏中最小的、线性排列的心肌细胞自然聚集物。它们是研究体外完整心肌功能的首选材料。在体内，心肌小梁的独特之处在于它们可以从两个独立的来源获得氧气：冠状动脉循环和周围的心室血液。由于冠状动脉小动脉中的氧分压（PO2）在两个心室的标本中是相同的，而左心室的氧分压比右心室高 2.5 倍，因此心肌小梁代表了一个“天然实验室”，可以研究“血管外”PO2 对心肌组织毛细血管化程度的影响。我们利用这一优势来检验四个假设。（1）在左右心室的小梁中，细胞的外周环没有毛细血管。（2）因此，足够小的左右心室小梁完全没有毛细血管。（3）来自左右心室的标本中的毛细血管与心肌细胞的比例与各自壁的比例相同。（4）来自左右心室的标本中的毛细血管与心肌细胞的比例具有可比性，反映了体内等效的能量需求，由相同的收缩频率和可比的壁应力驱动。我们应用共聚焦荧光成像技术对心肌小梁进行横切，随后使用半自动分割技术将毛细血管与心肌细胞区分开来。我们量化了左右心室小梁的毛细血管与心肌细胞的比例，并将其与心室游离壁和室间隔的比例进行了比较。通过使用椭圆横截面扩散方程的经典解以及适用于包含毛细血管和非呼吸胶原纤维任意排列的任意形状横截面的新方法，数学建模进一步促进了定量解释。
