[Heart fibroblasts, the mechanism of the appearance of their potentials and their possible role in regulating cardiac work]

Abstract

Electrically non-excitable fibroblasts, which represent the other population of cells abundant in the sino-atrial node region, have been reported to be mechanosensitive in the frog and in the rat heart. It was shown that these cells respond to artificial or contraction-induced stretch of the atrial wall by a change in membrane potential. These changes could be explained by the operation of stretch-activated channels and intracellular calcium oscillation. Influences of cardiac fibroblasts on electrophysiological properties of cardiomyocytes would require interaction between these cells. In tissue culture studies, it has been shown, that fibroblasts and cardiomyocytes form nexus connections. In recent studies on fibroblast-cardiomyocyte junctions in the rabbit heart pacemaker region, non nexus-like contacts clearly dominated. These membrane non nexus-like contacts might promote capacitive interactions between heterologous cells, which has been demonstrated independently in electrophysiological studies. Through these contacts, the fibroblast membrane potential may affect the membrane potential of neighbouring myocytes in the right atrium which may play an important role for the chronotropic response of the heart to mechanical stretch of the right atrial wall. Electrically non-excitable but mechanosensitive cardiac fibroblasts can act as a substrate for an intracardiac mechano-electrical feedback mechanism by which mechanical changes, e.g. stretch, modulate the electrical activity. In the atria, fibroblasts may act as volume and mechanical sensors, respectively.