Active force in rabbit ventricular myocytes

Although recent technical advances have established the feasibility of force measurements in single cardiac myocytes, the physiological relevance of this model has not been fully evaluated. We measured active force and sarcomere length in single rabbit left ventricular myocytes and compared their physiological responses to changes in stimulus interval, calcium concentration and sarcomere length to results from isolated papillary muscles. Myocytes were attached to two poly-L-lysine-coated glass plates and force was measured with a capacitive force transducer (Cambridge 406A). Stable recordings from a continuously contracting myocyte could be maintained for over 1 h. In five cells, increasing stimulus interval significantly decreased active force development. This force-stimulus interval relation was similar to that obtained from papillary muscles. In one cell, we obtained a force-length relation that was similar to force-length relations from multicellular preparations. Active stresses (active forces normalized by cross-sectional area) were of similar magnitude when comparing myocytes (at slack length) and papillary muscles (at 85% of Lmax). These results confirm the physiological relevance of force measurements obtained from intact mammalian cardiac myocytes.