HL-1 cells are famous for being the only contracting cell-line. They proliferate while keeping a differentiated cardiomyocyte phenotype. However, concerns about their genetic stability is considerable. Keeping them beating passage after passage is very tricky (any tips on that?). The increasing population of non-beating cells in the culture have different metabolic profiles and have basically lost the only advantage of these cells.
On the other hand, H9c2 cells are much cheaper and easier to maintain. But they are undifferentiated myoblasts, so they do not contract and are generally considered less relevant to cardiomyocytes.
Any ideas about which one is preferred over the other?