Isolated rat thoracic aorta which is pharmacologically precontracted by phenylephrine induces photorelaxation when exposed to long wave length UV-light. The aim of the present study was to characterize the mechanism of UV-light induced by photorelaxation in the rat aorta. 1. UV light relaxed both endothelium-intact and -denuded rat aortic rings contracted by phenylephrine. The magnitude of relaxation on UV light was dependent on the exposure time and slightly greatly in endothelium-denuded rings than in endothelium-intact preparations. 2. L-NAME (10 nM-100 uM) but not D-NAME completely inhibited the photorelaxation in a concentration dependent manner. 3. The UV-induced relaxation was inhibited by methylene blue (1 -100 uM), and verapamil (100 nM), and removal of extracellular Ca2+. In contrast, UV-light induced photorelaxation was potentiated by N(w)-nitro-Larginine (L-NOARG) treatment. 4. In immunocytochemical analysis of UV-light induced iNOS and eNOS expression in rat aortas, at which expression levels were increased in a time-dependent manner on UV-irradiation in aortic endothelium and smooth muscle, respectively. These results suggest that UV light-induced photorelaxation may be due to nitric oxide from exogenously administered L-arginine as well as endogenous nitric oxide donors such as amino acid and arginine derivatives. Additional suggestion is that UV light stimulates the expression of nitric oxide synthases, and its activity for nitric oxide generation is dependent on cytosolic Ca2+ originated from extracellular space.
Acetylcholine/pharmacology ; Animals ; Aorta, Thoracic/drug effects/*physiology/radiation effects ; Calcium Channel Blockers/pharmacology ; Cholinergic Agents/pharmacology ; Endothelium, Vascular/drug effects/physiology/radiation effects ; Enzyme Inhibitors/pharmacology ; Female ; Male ; Methylene Blue/pharmacology ; NG-Nitroarginine Methyl Ester/pharmacology ; Nitric Oxide Synthase/antagonists & inhibitors/metabolism ; Phenylephrine/pharmacology ; Rats ; Rats, Sprague-Dawley ; *Ultraviolet Rays ; Vasoconstrictor Agents/pharmacology ; Vasodilation/drug effects/*radiation effects ; Vasodilator Agents/pharmacology ; Verapamil/pharmacology

The goal of the present study was to investigate the effects of quercetin-filled phosphatidylcholine liposomes (PCL-Q) on the currents carried by large conductance Ca(2+)-dependent K(+) channels (BK(Ca)) in rat thoracic aorta following non-fatal whole-body ionizing irradiation. Using patch-clamp technique, it is found that the outward K(+) currents of isolated smooth muscle cells (SMCs) stimulated by depolarizing voltage steps were sensitive to BK(Ca) inhibitor, paxilline, and this kind of outward K(+) currents in SMCs from irradiated animals demonstrated a significant decrease in amplitude. Radiation-induced BK(Ca) suppression was evident 9 days post-irradiation and progressively increased over 30 days of experimental period. Thus, the vasorelaxing force of these SMCs may be diminished following irradiation. PCL-Q effectively restored BK(Ca) function in post-irradiated SMCs. It is noteworthy that the constituents of PCL-Q, i.e., free quercetin (Q) and "empty" liposomes (PCL), being taken separately, showed a decreased ability to recover BK(Ca) function as compared with combined composition. These results suggest that PCL-Q is able to regain normal function of BK(Ca) following irradiation. The protective effects of PCL-Q can be explained by its antioxidant and membrane repairing properties as well as its ability to inhibit protein kinase C activity. Thus, the lipid encapsulation of flavonoid, PCL-Q, appears to be a potential medication in the case of ionizing irradiation accident, and for the patients with neoplasm who have to receive external radiotherapy as well.
Animals ; Aorta, Thoracic ; drug effects ; radiation effects ; Large-Conductance Calcium-Activated Potassium Channels ; physiology ; Liposomes ; chemistry ; Myocytes, Smooth Muscle ; physiology ; Patch-Clamp Techniques ; Phosphatidylcholines ; chemistry ; Quercetin ; pharmacology ; Radiation, Ionizing ; Rats