Temperature gradients in an in vitro motility assay. Changes in temperature (ΔT) generated by IR-laser irradiation were measured based on the changes in fluorescence intensity of rhodamine-labeled actin filaments. Three levels of gradients were adjusted by using neutral density filters: 60%, 50%, and 15% for high, medium, and low powers, respectively. Data are expressed as mean ± SEM. Error bars, <0.2°C (within plots). n = 3 for all power levels.