Mechanical measurements from isolated cardiac myocytes using a pipette attachment system.

Single rat left ventricular myocytes were attached at both ends using a newly described double-barreled micropipette technique. This attachment procedure enabled the measurement of the active and passive mechanical properties of chemically skinned cells that showed little structural deformation. The force and oscillatory stiffness (100 Hz) of the cells were measured with a high signal-to-noise ratio, and the sarcomere length throughout the entire cell was monitored using image analysis. The passive properties were investigated from the resting sarcomere length to > 3 microns. Analysis of the sarcomere behavior indicated a high level of homogeneity throughout the cell. The attachment method supported the full activation of the cells by increased free Ca2+ (pCa 4.5), which produced 22.3 mN/mm (mean sarcomere length 2.11 microns). A force/pCa relationship was determined, which, when fitted according to the Hill equation, gave parameters of nH = 2.62 and pCa50 = 5.58. The described techniques allow the accurate study of the mechanical properties of single myocytes with increased fidelity and reliability over the preexisting methods.