Structural coupling of cardiomyocytes and noncardiomyocytes: quantitative comparisons using a novel micropatterned cell pair assay.

Well-controlled studies of the structural and functional interactions between cardiomyocytes and other cells are essential for understanding heart pathophysiology and for the further development of safe and efficient cell therapies. We established a novel in vitro assay composed of a large number of individual micropatterned cell pairs with reproducible shape, size, and region of cell-cell contact. This assay was applied to quantify and compare the frequency of expression and distribution of electrical (connexin43) and mechanical (N-cadherin) coupling proteins in 5,000 cell pairs made of cardiomyocytes (CMs), cardiac fibroblasts (CFs), skeletal myoblasts (SKMs), and mesenchymal stem cells (MSCs). We found that for all cell pair types, side-side contacts between two cells formed 4.5-14.3 times more often than end-end contacts. Both connexin43 and N-cadherin were expressed in all homotypic CM pairs but in only 13.4-91.6% of pairs containing noncardiomyocytes, where expression was either junctional (at the site of cell-cell contact) or diffuse (inside the cytoplasm). CM expression was exclusively junctional in homotypic pairs but predominantly diffuse in heterotypic pairs. Noncardiomyocyte homotypic pairs exhibited diffuse expression 1.7-8.7 times more often than junctional expression, which was increased 2.6-4.4 times in heterotypic pairs. Junctional connexin43 and N-cadherin expression, respectively, were found in 38.6 +/- 7.3 and 39.6 +/- 6.2% of CM-MSC pairs, 21.9 +/- 5.0 and 13.6 +/- 1.9% of CM-SKM pairs, and in only 3.8-9.6% of CM-CF pairs. Measured frequencies of protein expression and distribution were stable for at least 4 days. Described studies in micropatterned cell pairs shed new light on cellular interactions relevant for cardiac function and cell therapies.