EFFECT OF FREE-RADICAL SCAVENGERS ON CHANGES IN ION CONDUCTANCE DURING EXPOSURE TO THERAPEUTIC ULTRASOUND

Ultrasound has been used in physical therapy for > 4 decades. Recent s tudies indicate that non-thermal mechanisms such as cavitation are inv olved in the observed effects. Free radicals and other highly reactive compounds are known to form during sonochemical reactions associated with acoustic cavitation. Using frog skin as a biological model, the p ossibility that the increase in ionic conductance (G(t)) upon exposure to therapeutic ultrasound is due to the effect of free radicals gener ated by sonochemical reactions, was investigated. It was found that th e presence of cystamine, cysteamine and sodium ascorbate significantly reduced the increase in conductance caused by the exposure to 300 mW/ cm(2) (1 MHz CW) therapeutic ultrasound. The attentuation in the effec ts was dependent on the concentration of the radical scavengers/antiox idants used, the incubation time, and the intensity of ultrasound. The effects were also dependent on the lipid solubility of free radical s cavengers/antioxidants. The time constant for the recovery process of G(t) in the presence of free radical scavengers and antioxidants after exposure to ultrasound was found to be not significantly different fr om control. These results suggest that the increase in G(t) due to ult rasound is induced by free radicals and other reactive species generat ed from acoustic cavitation. This study provides an indirect evidence to the contingent that free radicals are generated and act inside the cells. Furthermore, the radical scavengers and antioxidants used provi de protection from oxidative damage without being involved in the reco very of G(t) towards steady state values after sonication.