Mechanical and contractile properties of isolated single intact cardiac cells

In light of the demonstrated contractile and mechanical non-uniformities which exist in many of the commonly used intact cardiac preparations, there is now a recognized need to evaluate cardiac sarcomere performance directly in relatively simple cardiac preparations. The single cardiac cell represents the simplest intact cardiac preparation and it can provide the opportunity for relatively definitive studies of cardiac sarcomere performance, since the force at the sarcomere level is fairly well defined compared to the situation in more complex intact cardiac preparations and sarcomere lengths can be measured directly. Considerable progress has been made within the last five years in developing the methodology for preparing intact isolated single cardiac cells and for investigating the mechanical and contractile properties of these cells. There is now sufficient information available to warrant the conclusion that the isolated cardiac cell can have normal force generating and sarcomere shortening capacity as well as normal electrical activity. Studies on single cardiac cells have already given insight into the characteristics of 1) sarcomere shortening and extension at essentially zero external force, 2) sarcomere shortening during auxotonic force development, 3) the contribution which the cell makes to the resting tension-sarcomere length relationship of intact cardiac tissue, and 4) the sarcomere length-dependency of the force generating capacity of cardiac muscle during twitch contractions. These studies have also clearly demonstrated that the cardiac sarcomere has some type of a force-velocity relationship although the exact nature of this relationship remains to be determined.