Residual Force Enhancement in Mechanically Isolated Half-sarcomeres

Our goal was to test if half-sarcomeres produce force enhancement after stretch. Single myofibrils from rabbit psoas were placed in a temperature-controlled (10°C) bath, where half-sarcomeres were isolated using two precalibrated glass micro-needles. The force produced during activation of the half-sarcomere was measured by tracking the displacement of the micro-needles. The half-sarcomere length (HSL) variation was extracted by interpolating the displacement of the needles from the initial to the final distances measured from the Z-line to the center of the sarcomere. The steady-state forces after stretch were higher than the forces produced during the isometric contraction at the corresponding lengths. Force enhancement in halfsarcomeres cannot be attributed non-uniformity.