Optical forced oscillation for the study of lectin-glycoprotein interaction at the cellular membrane of a Chinese hamster ovary cell.

We report the application of a set of twin optical tweezers to trap and oscillate a ConA (lectin)- coated polystyrene particle and to measure its interaction with glycoprotein receptors at the cellular plasma membrane of a Chinese hamster ovary (CHO) cell. The particle was trapped between two quadratic potential wells defined by a set of twin optical tweezers and was forced to oscillate by chopping on and off one of the trapping beams. We tracked the oscillatory motion of the particle via a quadrant photodiode and measured with a lock-in amplifier the amplitude of the oscillation as a function of frequency at the fundamental component of the driving frequency over a frequency range from 10Hz to 600Hz. By analyzing the amplitude as a function of frequency for a free particle suspended in buffer solution without the presence of the CHO cell and compared with the corresponding data when the particle was interacting with the CHO cell, we deduced the transverse force constant associated with the optical trap and that associated with the interaction by treating both the optical trap and the interaction as linear springs. The force constants were determined to be approximately 2.15pN/mum for the trap and 2.53pN/mum for the lectin-glycoprotein interaction. When the CHO cell was treated with lantrunculin A, a drug that is known to destroy the cytoskeleton of the cell, the oscillation amplitude increased with time, indicating the softening of the cellular membrane, until a steady state with a smaller force constant was reached. The steady state value of the force constant depended on the drug concentration.