Cardiac myocyte stiffness following extraction with detergent and high salt solutions

Myocytes were prepared from enzymatically digested adult rat hearts and attached to concentric double-barreled suction micropipettes. Myocyte stiffness was calculated as the ratio of the oscillatory tension-to-strain amplitude, where the strain was produced by an applied 5-Hz perturbation. Stiffness, as a function of cell length, was measured in relaxing solution (pCa = 9) as the control solution, 0.5% Triton X-100 detergent, 0.47 M KCl, and 0.6 M KI. Ultrastructure of unattached cells in each solution is illustrated with electron micrographs. The dependence of cell stiffness on cell length was described by an exponential relation with a length constant that increased slightly in detergent, whereas the stiffness at control length appeared to fall. The major fall in absolute stiffness occurred with myosin extraction in KCl. Both the stiffness at control length and the slope of the ln stiffness-to-length relation declined with the disappearance of the A band. A further, but smaller, decline of stiffness occurred with KI extraction of the thin filaments. A highly compliant "ghost" remained after KI extraction but the stiffness-to-length relation was still measurable. The fall in stiffness with myosin extraction is discussed in relation to cytoskeletal filaments (titin, nebulin, and intermediate filaments.