An optical monitor of tension for small cardiac preparations.

When a light beam is focused on a muscle preparation which is allowed to contract, large changes in the intensity of the emerging light accompany the contraction. These movement-related optical signals were studied and compared to simultaneous measurements of force in isolated cardiac Purkinje fibers. The two signals were compared in response to action potentials and to graded changes in membrane potential controlled under voltage clamp. These experiments indicate that the optical signal is a sensitive monitor of tension development under these conditions. This technique is particularly well-suited to force measurements in smaller preparations in which direct mechanical techniques are not feasible.