Do low-power lasers change phase transition temperature of dipalmitoyl phosphatidylcholine (DPPC) membrane?

This study was designed to investigate the effects of the He-Ne laser (632.8 nm of wavelength, 8.5 mW in power, Senko Med. Co. Ltd., Tokyo, Japan) on the phase transition temperature of dipalmitoyl phosphatidylcholine (DPPC) membranes. Liposomal bilayers of DPPC (12.5 mM) were obtained with ultrasonification for 45 min at 40 degrees C and refrigerated for 2-3 days at 5 degrees C. The bilayers vesicle solution was divided into 3-ml working aliquots, which were assigned to three groups. The aliquots in Group 1 were used as controls without irradiation and the aliquots in Groups 2 and 3 were irradiated in 37 degrees C baths for 15 to 30 min, respectively. To determine phase transition temperature, optical density (%T; percent of permittance) of each aliquot was measured spectrophotomechanically at a wavelength of 440 nm while increasing its temperature at a rate of 0.5 degrees C every minute. Main phase transition temperatures in Groups 1, 2, and 3 were 41.54 +/- 0.23 degrees C (n = 10), 41.50 +/- 0.27 degrees C (n = 10), and 41.30 +/- 0.36 degrees C (n = 10), respectively. No significant difference between the nonirradiation and irradiation groups was established. These results suggest that irradiations of low-power He-Ne lasers up to 30 min do not change important physical characteristics of artificial DPPC membranes.