Fig. 3. Force-frequency relations of trabeculae at 1.36 mm (A ) and 0.5 mm (B ) Ca²⁺. Steady state forces were normalized to control force at 1 Hz. Open circles represent relative force during control conditions. Filled circles represent relative forces in the presence of 20 μg/ml propofol. At 1.36 mm Ca²⁺, propofol had a significant negative inotropic effect at 1 and 2 Hz but no effect at lower frequencies. At 0.5 mm Ca²⁺, propofol had a significant negative inotropic effect at 0.5, 1, and 2 Hz but a significant positive inotropic effect at 0.1 Hz (mean ± SEM).