Focus on cardiac pericytes.

The wall of myocardial terminal vessels, consisting of a continuous endothelial tube with an adventitial coat of pericytes in their extracellular matrix, constitutes a remarkably tight barrier to solute transport between the blood and the parenchyma. This constructional principle of precapillary arterioles, capillaries and postcapillary venules extends both up- and downstream into the arterial and venous limbs, where the original microvessel tube widens and becomes the innermost layer-the intima-of all the larger coronary vessels. In the myocardium's smallest functional units and in the intima of the coronaries, the pericytes play key roles by virtue of both their central histological localization and their physiological functions. Recognition and integration of these properties has led to new pathogenetic models for diverse heart diseases and suggests that current therapeutic concepts need to be revised.