Characterization of ultraviolet light-induced relaxation of the isolated duodenum of the rat.

1 Isolated duodenum of the rat, exposed to ultraviolet (u.v.) light in the presence of NO2 ions, responded with reversible relaxation. 2 The photorelaxation response did not seem to involve any known receptor mechanisms and was independent of any ganglionic or neuronal influences. 3 Changes in the ionic environment of the tissue showed that NA+ and Ca2+ were essential for the photorelaxation. K+ depolarized-tissue did not show the photoresponse. 4 The presence of the metabolic inhibitors, iodoacetic acid, 2,4-dinitrophenol, sodium fluoride, sodium azide or potassium cyanide, abolished the photorelaxation response. 5 It is proposed that the photorelaxation of the tissue resulted from the liberation of metabolic energy following NO2 ion-dependent absorption of u.v. light energy, which in turn, interfered with the Na+ ion movement across the cell membrane.