Our recent work suggests a critical role for b1 integrins in linking the cytoskeleton and G protein-coupled signaling clusters. Aim of this study was to investigate the role of the cytoplasmic part of b1 integrins for cardiac function using ILK deficient (-/-) ES cells. ILK is a key molecule which interacts with the actin cytoskeleton and with the b1-integrin cytoplasmic domain. ES cell-derived differentiation into atrial, ventricle and nodal like-carediomyocytes proved intact in both ILK (-/-) and wt cells. Interestingly, immunohistochemistry with a-actinin revealed that ILK (-/-) cardiomyocytes have an altered sarcomeric organization in the border zone of the cells.

Moreover, deconvolution imaging for the key basement membrane (BM) proteins Collagen IV, Perlecan and Laminin, depicted defects in BM formation in the ILK (-/-) ES cell-derived cardiomyocytes. Surprisingly, despite these alterations of the cytoskeleton and BM, we could detect at the single-cell level intact muscarinic signalling. Accordingly, the subcellular distribution of Gai was not dramatically altered in the ILK (-/-) cells. Thus, lack of ILK induces modifications of the sarcomeric structure and affects BM stability of cardiomyocytes, but does not interfere with the differentiation of cardiomyocytes and hormonal modulation.