Helium‐Neon laser irradiation of hepatocytes can trigger increase of the mitochondrial membrane potential and can stimulate c‐fos expression in a Ca2+‐dependent manner

Background and Objective To gain some insight into the photostimulation of isolated hepatocytes irradiated with Helium-Neon (He-Ne) laser light certain biochemical events were studied with respect to two mechanisms: i) the direct light dependent activation of certain biochemical events investigated in intact cells and isolated mitochondria, ii) the indirect stimulation of processes per se light independent. Study Design/Materials and Methods Irradiation of either isolated hepatocytes or isolated rat liver mitochondria was carried out with He-Ne laser (wavelength, 632.8 nm; fluence, 0.24 J cm−2; fluence rate, 12 mW cm−2). Changes in mitochondrial membrane potential in isolated hepatocytes were monitored using the cationic probe safranine. The c-fos expression was studied by Northern blot and immunoblot analysis. Results As a result of irradiation, increase of the mitochondrial membrane potential was found to occur in irradiated hepatocytes both in the presence or in the absence of CaCl2. The hyperpolarization of the mitochondrial membrane is assumed to cause an increase in mitochondrial Ca2+ uptake that was measured in isolated mitochondria. Finally, an increase in c-fos expression was found in irradiated hepatocytes when incubated in the presence of CaCl2. Conclusion This paper gives additional information on the mechanism by which He-Ne laser light, either directly or in a cascade-like effect dependent on increase in cell Ca2+, can cause cell stimulation. Lasers Surg. Med. 29:433–441, 2001. © 2001 Wiley-Liss, Inc.