1. Fig. 1. Cardiac, i.e., endocardial (EE) and myocardial capillary (MyoCapE), endothelium and myocardium. The ventricular wall (inset) consists of the epicardium, the myocardium, and the endocardium. The endocardium includes a fibroelastic layer, a basement membrane, and a luminal layer of endothelial cells, i.e., the EE [top left transmission electron microscopy (TEM) micrograph]. The distance between the MyoCapE (top right TEM micrograph) and cardiomyocytes is usually <1 μm; between EE and cardiomyocytes, the distance ranges from 1 μm in small mammals to >50 μm in humans. Analogous, and additive, myocardial actions of EE and MyoCapE result in contractile twitch prolongation and increased peak force development. The traces in the bottom panel represent isometric twitches (forcef vs. time t traces) from isolated papillary muscles with intact EE and MyoCapE, compared with twitches from muscles after selective EE damage (−EE) by quick immersion of the papillary muscle in 0.5% Triton X-100 and to twitches from muscles with MyoCapE dysfunction (−VE) induced by a bolus injection of diluted Triton X-100 in a Langendorff heart before isolation of the papillary muscle. Endothelial damage or dysfunction induced premature relaxation and concomitantly decreased peak force development. [Modified from Brutsaert et al. (60).]
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