Adult rat cardiomyocytes (ARC) were cultivated on five different substrates: gelatin, fibronectin, laminin-nidogen complex (laminin), the E8 laminin fragment, and the E1 laminin fragment. Comparative cell attachment assays have shown that ARC prefer adhesion to Eg laminin fragment and laminin. It were shown by video time-lapse (VTL) studies that, during the redifferentiation process of ARC in culture, the morphology of ARC grown on laminin, fibronectin, and gelatin is indistinguishable, whereas the size of ARC grown on the E8 fragment is larger, and when grown on the E1 fragment definitely smaller than ARC on the whole laminin protein. Immunostaining for vinculin combined with reflection contrast microscopy were used to visualize the focal contacts of ARC on these substrates. Quantitative measurements, done with the help of a test line system, show that the lengths of adhesion plaques/mu m(2) on gelatin, fibronectin, and laminin are about the same. On the E8 fragment more attachment sites/mu m(2) and on the E1 fragment fewer attachment sites/mu m(2) were counted than on whole laminin protein. This suggests that substrates influence the number of focal contacts. Correlating these results with the observations made in the VTL recording system, one can suggest that the length of adhesion sites/mu m(2) increases in very hat and large cells. (C) 1994 Academic Press, Inc.