Vascular interactions of calcium and reactive oxygen intermediates produced following photoradiation

This study was designed to examine vascular smooth muscle contractile properties following enhanced production of reactive oxygen intermediates (ROIs), which were produced by pretreating rat caudal arteries and aortas with a photosensitizer, hematoporphyrin derivative, and then illuminating them with red laser light. This treatment produced a long-lasting contraction that was dependent on the presence of extracellular calcium. Reduction in extracellular calcium relaxed the smooth muscle and replacement of calcium 30 min later increased the tension. Oxygen radical scavengers did not block the contractile effect postillumination when calcium was returned to the bathing solution; however, verapamil (5.5 microM) and nifedipine (10 microM) attenuated this contraction. The contractions were dependent on oxygen in the aerating gas mixture. Production of ROIs by isolated blood vessels was supported biochemically by a significant increase in both bath and tissue levels of oxidation products, reactive with thiobarbituric acid, and by a reduction in the tissue stain, nitroblue tetrazolium. These ROI-induced contractions were observed in vitro on large conduit arteries and also in vivo on small ear arteries. The vascular response following this acute production of ROIs may be similar to vascular abnormalities in certain pathological conditions where ROI production is reported to be elevated. Therefore, these results could contribute to a further understanding of mechanisms involved in these ROI-dependent vascular changes.