The NO donors added to the cellular suspension before irradiation eliminate the radiation-induced increase in the number of cells attached to the glass matrix, supposedly by way of binding NO to cytochrome c oxidase. NO added to the suspension after irradiation can also inhibit the light-induced signal downstream. Both effects of NO depend on the concentration of the NO donors added. These results indicate that NO can control the irradiation-activated reactions that increase the attachment of cells.
The number of cells attached to glass substratum increases if HeLa cell suspension is irradiated with monochromatic visible-to-near infrared radiation before plating (the action spectrum with maxima at 619, 657, 675, 700, 740, 760, 800, 820, 840 and 860 nm). Treating of cell suspension with sodium azide (2 x 10(-5) M), sodium nitroprusside (5 x 10(-5) M), ouabain (1 x 10(-6) M) or amiloride (1.7 x 10(-5) M) before irradiation significantly modifies the spectrum of cell attachment enhancement. A light-induced mitochondrial signaling pathway can be regulated by small ligands directly binding to the catalytic center of cytochrome c oxidase (N(3), NO) as well as by chemicals specifically binding to plasma membrane enzymes (ouabain, amiloride). The comparative analysis of action spectra allows the conclusions that first, Cu(A) and Cu(B) chromophores of cytochrome c oxidase could be involved as photoacceptors and second, various signaling pathways (reaction channels) between cytochrome c oxidase and cell attachment regulation are at work.
The experimental results of our work demonstrate that irradiation at 632.8 nm causes either a (transient) relative reduction of the photoacceptor, putatively cytochrome c oxidase, or its (transient) relative oxidation, depending on the initial redox status of the photoacceptor. The maximum in the bell-shaped dose-dependence curve or the minimum of the reverse curve is the turning point between the prevailing of oxidation or reduction processes. Our results are evidence that the bell-shaped dose dependences recorded for various cellular responses are characteristic also for redox changes in the photoacceptor, cytochrome c oxidase.
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