Incorrect DNA repair is probably one cause of healthy ageing. Laser microbeams or optical tweezers are emerging as convenient tools in the study of repair mechanisms. Using such tools, DNA damage can be induced in a preselected volume element of a cell nucleus and at a preselected time point - an effect which is hardly to achieve with any other tool. On the other hand damage induction highly depends on a subtle combination of laser mircobeam parameters such as dose, pulse peak power and wavelength. In consequence DNA repair at the sites of damage may work differently. Furthermore, such sites are occasionally stationary, occasionally they migrate towards each other, indicating a considerable dynamics of DNA repair inside a cell nucleus. As an example for the application of optical tweezers, Erythrocyte Mediated Force Application (EMFA) is used to induce nitric oxide production in cells of the endothelium, i. e. the inner layer of (human) blood vessels. It is shown that upon stimulation by EMFA, endothelial cells initially activate the calcium homeostasis and develop calcium humps, concentration plateaus and oscillations.