Cell membrane molecular dynamics under a NIR focused laser

Light interaction with live cells can lead to important effects. Near infrared (NIR) lasers are used in therapies to diminish inflammation and pain. In a microscopic scale, NIR laser light has been used to stimulate and guide the growth of cells like neurons and fibroblasts. However, it is still unclear what NIR laser radiation provokes to the cells at the molecular and biophysical levels. In this contribution we report the effects of a continuous wave 810-nm laser on the plasma membrane of in vivo 3T3 fibroblast cells. Membranes were labelled the lipophilic styryl dye FM 4-64 and imaged by confocal microscopy. We found that the NIR laser produces an increase of the fluorescence intensity at the location of laser spot. This intensity boost vanishes when the laser is turned off. The time taken by the increase and decrease is of the order of 10 seconds. The mean fluorescence increase, calculated over 75 independent measurements, equals 19%. The experiments reveal that the fluorescence rise is a growing function of the laser power. This dependence is well fitted with a square root function. The NIR laser provokes a rise in the number of molecular associations dye-lipid. The results reported here may be a consequence of a combination of induced increments in membrane fluidity and exocytosis. To the best of our knowledge, this is the first demonstration of the influence of focused NIR laser on the lipid dynamics of a live cell plasma membrane.