Helium‐Neon laser irradiation inhibits the growth of kidney epithelial cells in culture

We have investigated the in vitro action of helium‐neon (He‐Ne) laser light on the cell cycle and the growth of rat kidney epithelial cell cultures. Dose‐response studies showed that repeated He‐Ne irradiation (dose rate 40 mW/cm²) once a day in a dose range between 11.9 and 142 J/cm² significantly inhibited cell growth, while daily irradiation with 4.7 J/cm² had no effect. Microscopic examination of nuclear spreads revealed an increased number of cells in mitosis after a single irradiation with 142 J/cm². These results support previous observations suggesting that laser light of low thermal energy interferes with cell cycling and may inhibit cell growth when irradiation is performed at doses of 11.9 J/cm² or more.