Abstract:
Trabeculae (from the Greek for ‘little planks’) are minute, naturally-arising collections of cardiac myocytes — much utilised in studies of the mechanical behaviour of the heart. It is surprising that, despite some three decades of such use, their microstructure has not been examined in detail. We have rectified this deficit by performing quantitative confocal, laser-scanning, microscopy on cross-sections of Bouins-fixed, picrosirius-red-stained specimens selected from both the right (n = 9) and left (n = 12) ventricles of adult rat hearts. Trabecula cross-section tended to become less circular (i.e., more elliptical) with increasing size. In no case did we observe preparations that could be considered ‘ribbon-like’ or ‘slab-shaped’, as classically described. We quantified the relative proportions of blood vessels, myocytes and collagen. These were 2%, 79% and 19%, respectively, for left-ventricular trabeculae and 4%, 70% and 26% for those from the right ventricle. Our particular focus was on the ratio of the number of capillaries (vessels less than 5 μm in diameter) to the number of myocytes. The value of this ratio, for trabeculae from either ventricle, was approximately 0.5. By contrast, the capillary-myocyte ratio was approximately 1.0 for the left-ventricular wall and 0.8 for both the right-ventricular wall and the interventricular septum. From these results, we infer that myocytes in the outermost annulus of a trabecula must receive their oxygen supply primarily from the ventricular blood in which they are bathed, rather than from the coronary circulation. If this inference is correct, then this renders trabeculae even better in vitro models of ventricular wall tissue than previously realised.