Quantitative microstructure of rat right-ventricular trabeculae carne

Abstract

Due to their small diameter and the axial alignment of their myocytes, isolated trabeculae carnae are extensively used in studies of the mechanics of cardiac tissue. An understanding of their structure is essential for the interpretation of results arising from such studies. Our aim was to quantify the relative proportions of myocytes, connective tissue and blood vessels constituting right-ventricular trabeculae carnae from adult rats. Isolated hearts were Langendorff-perfusion fixed with 3% formalin in high osmolarity phosphate buffer. A trabecula was dissected from the ventricular free wall and embedded in a resin block. The block was fixed onto the translation stage of an extended-volume imaging system (1) and its surface milled to expose the preparation in cross-section. The exposed surface was etched (2), stained with toluidine blue (for myocytes), followed by ponceau de xylidine and acid fuchsin (for connective tissue), and photographed using a digital camera attached to a compound light microscope with a 20x, 0.7 NA, water-immersion lens. The samples were milled at 20 μm intervals to obtain a series of sequential cross-sectional images. In order to calculate fractional areas, images were segmented, based upon colour and intensity differences. The relative areas (mean ± 95% confidence limits, n = 8) were: 0.77 ± 0.028 myocytes, 0.11 ± 0.030 collagen and 0.11 ± 0.018 blood vessels. With the exception of those in the peripheral layer, essentially every myocyte had at least one immediately adjacent capillary while, on average, each capillary serviced two myocytes. Three-dimensional reconstruction (at 1 μm intervals) of a 50 μm segment revealed that most axially-aligned capillaries are interconnected, at some point, forming a reticulated microvascular network within the trabecula.