ACTIVE FORCE IN RABBIT VENTRICULAR MYOCYTES

Although recent technical advances have established the feasibility of force measurements in single cardiac myocytes, the physiological rele vance of this model has not been fully evaluated. We measured active f orce and sarcomere length in single rabbit left ventricular mycocytes and compared their physiological responses to changes in stimulus inte rval, calcium concentration and sarcomere length to results from isola ted papillary muscles. Myocytes were attached to two poly-L-lysine-coa ted glass plates and force was measured with a capacitive force transd ucer (Cambridge 406A). Stable recordings from a continuously contracti ng myocyte could be maintained for over 1 h. In five cells, increasing stimulus interval significantly decreased active force development. T his force-stimulus interval relation was similar to that obtained from papillary muscles. In one cell, we obtained a force-length relation t hat was similar to force-length relations from multicellular preparati ons. 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 L(max)). These results confirm the ph ysiological relevance of force measurements obtained from intact mamma lian cardiac myocytes.