Firing inhibition processes in the response dynamics of isolated crayfish nerve cell to the photodynamic effect of sulphonated aluminium phthalocyanine: Participation of free radicals and Ca2+

Chemical modifications allows the enhancement or attenuation of the cell re sponse to photo dynamic effect and provides information on the mechanisms o f this effect. Isolated crayfish neurons were incubated for 30 min with 10( -7) M Photosens (AlPcSn) and irradiated by He-Ne laser (632.8 nm, 0.3 W/cm( 2)). Such treatment caused firing inhibition until it was irreversibly abol ished. The antioxidants homocarnosine, DABCO or ascorbate, pro-oxidant, FeS O4 or a mixture of FeSO4 and ascorbate; Ca2+ modulators, CdCl2, verapamil, EDTA, dantrolene, caffeine, theophylline, or a threefold CaCl2 concentratio n were used to modify neuron response (firing inhibition and abolition). Ho mocarnosine, CdCl2, DABCO, dantrolene, and caffeine or theophylline added 3 0-90 min before irradiation, increased neuron lifetime under the photodynam ic effect of Photosens whereas FeSO4/ascorbate, EDTA, threefold Ca2+ concen tration or caffeine (added 5 min before irradiation) decreased neuron lifet ime. It is concluded that, free radical processes and Ca2+ participate in t he Photosens-induced photodynamic inhibition and subsequent irreversible ab olition of neuron firing.