Motorcycle Exhaust Particulates Enhance Vasoconstriction in Organ Culture of Rat Aortas and Involve Reactive Oxygen Species

The effects of motorcycle exhaust particulate on vasoconstriction were determined using rat thoracic aortas under organ culture conditions treated with organic extracts of motorcycle exhaust particulate from a two-stroke engine. The motorcycle exhaust particulate extract (MEPE) induced a concentration-dependent enhancement of vasoconstriction elicited by phenylephrine in the organ cultures of both intact and endothelium-denuded aortas for 18 h. Nifedipine (an L-type Ca2+ channel blocker), manganese acetate (an inorganic Ca2+ channel blocker), and staurosporine (a nonselective protein kinase C inhibitor), but not the selective protein kinase C inhibitor chelerythrine, inhibited the enhancement of vasoconstriction by MEPE. Staurosporine has also been reported as a myosin light chain kinase (MLCK) inhibitor, so we tested whether the MLCK pathway was involved in the effect of MEPE. The results showed that ML-9 (a selective MLCK inhibitor) could inhibit the enhancement of vasoconstriction by MEPE. The phosphorylation of a 20-kDa myosin light chain in a primary culture of rat vascular smooth muscle cells was also enhanced by MEPE. Moreover, we also examined the role of reactive oxygen species (ROS) in the stimulatory effect of MEPE on vasoconstriction. The antioxidant N-acetylcysteine significantly inhibited the enhancement of vasoconstriction by MEPE. A time-dependent increase in ROS production by MEPE was also detected in primary cultures of vascular smooth muscle cells. These results indicate that MEPE induces a marked enhancement of vasoconstriction in aortas under organ culture conditions and imply that a ROS-Ca2+-MLCK pathway may be involved in this MEPE-induced response.