Heterogeneous cell coupling in the heart: an electrophysiological role for fibroblasts. Circ Res

The heart is a muscle. Muscles are made up of myo-cytes. These may differ in form and function, but—inessence—they are the cells in which we are interested when we consider the structural makeup of the heart. Like-wise, when we assess electrical coupling of cardiac cells by connexins, we are often content to assume that gap junctions occur exclusively—or at least in the overwhelming majority of cases—between homologous cell types. It is sobering, in this context, to reflect on the fact that cardiac myocytes form a minority of cells in the heart, insofar as cell numbers are concerned (which, for cell coupling, is more relevant than total volume occupied by a cell popula-tion). A meticulous study by Adler et al1 demonstrated that myocyte and connective tissue cell numbers increase at a similar rate in early human development, from about 0.5109 at 28 weeks of fetal development to 2 to 3109 several weeks postpartum. Thereafter, myocyte cell numbers remain stable